1	// SPDX-License-Identifier: GPL-2.0-only
2	/*
3	* Memory merging support.
4	*
5	* This code enables dynamic sharing of identical pages found in different
6	* memory areas, even if they are not shared by fork()
7	*
8	* Copyright (C) 2008-2009 Red Hat, Inc.
9	* Authors:
10	* Izik Eidus
11	* Andrea Arcangeli
12	* Chris Wright
13	* Hugh Dickins
14	*/
15
16	#include <linux/errno.h>
17	#include <linux/mm.h>
18	#include <linux/mm_inline.h>
19	#include <linux/fs.h>
20	#include <linux/mman.h>
21	#include <linux/sched.h>
22	#include <linux/sched/mm.h>
23	#include <linux/sched/coredump.h>
24	#include <linux/rwsem.h>
25	#include <linux/pagemap.h>
26	#include <linux/rmap.h>
27	#include <linux/spinlock.h>
28	#include <linux/xxhash.h>
29	#include <linux/delay.h>
30	#include <linux/kthread.h>
31	#include <linux/wait.h>
32	#include <linux/slab.h>
33	#include <linux/rbtree.h>
34	#include <linux/memory.h>
35	#include <linux/mmu_notifier.h>
36	#include <linux/swap.h>
37	#include <linux/ksm.h>
38	#include <linux/hashtable.h>
39	#include <linux/freezer.h>
40	#include <linux/oom.h>
41	#include <linux/numa.h>
42	#include <linux/pagewalk.h>
43
44	#include <asm/tlbflush.h>
45	#include "internal.h"
46	#include "mm_slot.h"
47
48	#define CREATE_TRACE_POINTS
49	#include <trace/events/ksm.h>
50
51	#ifdef CONFIG_NUMA
52	#define NUMA(x) (x)
53	#define DO_NUMA(x) do { (x); } while (0)
54	#else
55	#define NUMA(x) (0)
56	#define DO_NUMA(x) do { } while (0)
57	#endif
58
59	/**
60	* DOC: Overview
61	*
62	* A few notes about the KSM scanning process,
63	* to make it easier to understand the data structures below:
64	*
65	* In order to reduce excessive scanning, KSM sorts the memory pages by their
66	* contents into a data structure that holds pointers to the pages' locations.
67	*
68	* Since the contents of the pages may change at any moment, KSM cannot just
69	* insert the pages into a normal sorted tree and expect it to find anything.
70	* Therefore KSM uses two data structures - the stable and the unstable tree.
71	*
72	* The stable tree holds pointers to all the merged pages (ksm pages), sorted
73	* by their contents. Because each such page is write-protected, searching on
74	* this tree is fully assured to be working (except when pages are unmapped),
75	* and therefore this tree is called the stable tree.
76	*
77	* The stable tree node includes information required for reverse
78	* mapping from a KSM page to virtual addresses that map this page.
79	*
80	* In order to avoid large latencies of the rmap walks on KSM pages,
81	* KSM maintains two types of nodes in the stable tree:
82	*
83	* * the regular nodes that keep the reverse mapping structures in a
84	* linked list
85	* * the "chains" that link nodes ("dups") that represent the same
86	* write protected memory content, but each "dup" corresponds to a
87	* different KSM page copy of that content
88	*
89	* Internally, the regular nodes, "dups" and "chains" are represented
90	* using the same struct ksm_stable_node structure.
91	*
92	* In addition to the stable tree, KSM uses a second data structure called the
93	* unstable tree: this tree holds pointers to pages which have been found to
94	* be "unchanged for a period of time". The unstable tree sorts these pages
95	* by their contents, but since they are not write-protected, KSM cannot rely
96	* upon the unstable tree to work correctly - the unstable tree is liable to
97	* be corrupted as its contents are modified, and so it is called unstable.
98	*
99	* KSM solves this problem by several techniques:
100	*
101	* 1) The unstable tree is flushed every time KSM completes scanning all
102	* memory areas, and then the tree is rebuilt again from the beginning.
103	* 2) KSM will only insert into the unstable tree, pages whose hash value
104	* has not changed since the previous scan of all memory areas.
105	* 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
106	* colors of the nodes and not on their contents, assuring that even when
107	* the tree gets "corrupted" it won't get out of balance, so scanning time
108	* remains the same (also, searching and inserting nodes in an rbtree uses
109	* the same algorithm, so we have no overhead when we flush and rebuild).
110	* 4) KSM never flushes the stable tree, which means that even if it were to
111	* take 10 attempts to find a page in the unstable tree, once it is found,
112	* it is secured in the stable tree. (When we scan a new page, we first
113	* compare it against the stable tree, and then against the unstable tree.)
114	*
115	* If the merge_across_nodes tunable is unset, then KSM maintains multiple
116	* stable trees and multiple unstable trees: one of each for each NUMA node.
117	*/
118
119	/**
120	* struct ksm_mm_slot - ksm information per mm that is being scanned
121	* @slot: hash lookup from mm to mm_slot
122	* @rmap_list: head for this mm_slot's singly-linked list of rmap_items
123	*/
124	struct ksm_mm_slot {
125	struct mm_slot slot;
126	struct ksm_rmap_item *rmap_list;
127	};
128
129	/**
130	* struct ksm_scan - cursor for scanning
131	* @mm_slot: the current mm_slot we are scanning
132	* @address: the next address inside that to be scanned
133	* @rmap_list: link to the next rmap to be scanned in the rmap_list
134	* @seqnr: count of completed full scans (needed when removing unstable node)
135	*
136	* There is only the one ksm_scan instance of this cursor structure.
137	*/
138	struct ksm_scan {
139	struct ksm_mm_slot *mm_slot;
140	unsigned long address;
141	struct ksm_rmap_item **rmap_list;
142	unsigned long seqnr;
143	};
144
145	/**
146	* struct ksm_stable_node - node of the stable rbtree
147	* @node: rb node of this ksm page in the stable tree
148	* @head: (overlaying parent) &migrate_nodes indicates temporarily on that list
149	* @hlist_dup: linked into the stable_node->hlist with a stable_node chain
150	* @list: linked into migrate_nodes, pending placement in the proper node tree
151	* @hlist: hlist head of rmap_items using this ksm page
152	* @kpfn: page frame number of this ksm page (perhaps temporarily on wrong nid)
153	* @chain_prune_time: time of the last full garbage collection
154	* @rmap_hlist_len: number of rmap_item entries in hlist or STABLE_NODE_CHAIN
155	* @nid: NUMA node id of stable tree in which linked (may not match kpfn)
156	*/
157	struct ksm_stable_node {
158	union {
159	struct rb_node node; /* when node of stable tree */
160	struct { /* when listed for migration */
161	struct list_head *head;
162	struct {
163	struct hlist_node hlist_dup;
164	struct list_head list;
165	};
166	};
167	};
168	struct hlist_head hlist;
169	union {
170	unsigned long kpfn;
171	unsigned long chain_prune_time;
172	};
173	/*
174	* STABLE_NODE_CHAIN can be any negative number in
175	* rmap_hlist_len negative range, but better not -1 to be able
176	* to reliably detect underflows.
177	*/
178	#define STABLE_NODE_CHAIN -1024
179	int rmap_hlist_len;
180	#ifdef CONFIG_NUMA
181	int nid;
182	#endif
183	};
184
185	/**
186	* struct ksm_rmap_item - reverse mapping item for virtual addresses
187	* @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
188	* @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
189	* @nid: NUMA node id of unstable tree in which linked (may not match page)
190	* @mm: the memory structure this rmap_item is pointing into
191	* @address: the virtual address this rmap_item tracks (+ flags in low bits)
192	* @oldchecksum: previous checksum of the page at that virtual address
193	* @node: rb node of this rmap_item in the unstable tree
194	* @head: pointer to stable_node heading this list in the stable tree
195	* @hlist: link into hlist of rmap_items hanging off that stable_node
196	*/
197	struct ksm_rmap_item {
198	struct ksm_rmap_item *rmap_list;
199	union {
200	struct anon_vma *anon_vma; /* when stable */
201	#ifdef CONFIG_NUMA
202	int nid; /* when node of unstable tree */
203	#endif
204	};
205	struct mm_struct *mm;
206	unsigned long address; /* + low bits used for flags below */
207	unsigned int oldchecksum; /* when unstable */
208	union {
209	struct rb_node node; /* when node of unstable tree */
210	struct { /* when listed from stable tree */
211	struct ksm_stable_node *head;
212	struct hlist_node hlist;
213	};
214	};
215	};
216
217	#define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */
218	#define UNSTABLE_FLAG 0x100 /* is a node of the unstable tree */
219	#define STABLE_FLAG 0x200 /* is listed from the stable tree */
220
221	/* The stable and unstable tree heads */
222	static struct rb_root one_stable_tree[1] = { RB_ROOT };
223	static struct rb_root one_unstable_tree[1] = { RB_ROOT };
224	static struct rb_root *root_stable_tree = one_stable_tree;
225	static struct rb_root *root_unstable_tree = one_unstable_tree;
226
227	/* Recently migrated nodes of stable tree, pending proper placement */
228	static LIST_HEAD(migrate_nodes);
229	#define STABLE_NODE_DUP_HEAD ((struct list_head *)&migrate_nodes.prev)
230
231	#define MM_SLOTS_HASH_BITS 10
232	static DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
233
234	static struct ksm_mm_slot ksm_mm_head = {
235	.slot.mm_node = LIST_HEAD_INIT(ksm_mm_head.slot.mm_node),
236	};
237	static struct ksm_scan ksm_scan = {
238	.mm_slot = &ksm_mm_head,
239	};
240
241	static struct kmem_cache *rmap_item_cache;
242	static struct kmem_cache *stable_node_cache;
243	static struct kmem_cache *mm_slot_cache;
244
245	/* The number of nodes in the stable tree */
246	static unsigned long ksm_pages_shared;
247
248	/* The number of page slots additionally sharing those nodes */
249	static unsigned long ksm_pages_sharing;
250
251	/* The number of nodes in the unstable tree */
252	static unsigned long ksm_pages_unshared;
253
254	/* The number of rmap_items in use: to calculate pages_volatile */
255	static unsigned long ksm_rmap_items;
256
257	/* The number of stable_node chains */
258	static unsigned long ksm_stable_node_chains;
259
260	/* The number of stable_node dups linked to the stable_node chains */
261	static unsigned long ksm_stable_node_dups;
262
263	/* Delay in pruning stale stable_node_dups in the stable_node_chains */
264	static unsigned int ksm_stable_node_chains_prune_millisecs = 2000;
265
266	/* Maximum number of page slots sharing a stable node */
267	static int ksm_max_page_sharing = 256;
268
269	/* Number of pages ksmd should scan in one batch */
270	static unsigned int ksm_thread_pages_to_scan = 100;
271
272	/* Milliseconds ksmd should sleep between batches */
273	static unsigned int ksm_thread_sleep_millisecs = 20;
274
275	/* Checksum of an empty (zeroed) page */
276	static unsigned int zero_checksum __read_mostly;
277
278	/* Whether to merge empty (zeroed) pages with actual zero pages */
279	static bool ksm_use_zero_pages __read_mostly;
280
281	#ifdef CONFIG_NUMA
282	/* Zeroed when merging across nodes is not allowed */
283	static unsigned int ksm_merge_across_nodes = 1;
284	static int ksm_nr_node_ids = 1;
285	#else
286	#define ksm_merge_across_nodes 1U
287	#define ksm_nr_node_ids 1
288	#endif
289
290	#define KSM_RUN_STOP 0
291	#define KSM_RUN_MERGE 1
292	#define KSM_RUN_UNMERGE 2
293	#define KSM_RUN_OFFLINE 4
294	static unsigned long ksm_run = KSM_RUN_STOP;
295	static void wait_while_offlining(void);
296
297	static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
298	static DECLARE_WAIT_QUEUE_HEAD(ksm_iter_wait);
299	static DEFINE_MUTEX(ksm_thread_mutex);
300	static DEFINE_SPINLOCK(ksm_mmlist_lock);
301
302	#define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create(#__struct,\
303	sizeof(struct __struct), __alignof__(struct __struct),\
304	(__flags), NULL)
305
306	static int __init ksm_slab_init(void)
307	{
308	rmap_item_cache = KSM_KMEM_CACHE(ksm_rmap_item, 0);
309	if (!rmap_item_cache)
310	goto out;
311
312	stable_node_cache = KSM_KMEM_CACHE(ksm_stable_node, 0);
313	if (!stable_node_cache)
314	goto out_free1;
315
316	mm_slot_cache = KSM_KMEM_CACHE(ksm_mm_slot, 0);
317	if (!mm_slot_cache)
318	goto out_free2;
319
320	return 0;
321
322	out_free2:
323	kmem_cache_destroy(s: stable_node_cache);
324	out_free1:
325	kmem_cache_destroy(s: rmap_item_cache);
326	out:
327	return -ENOMEM;
328	}
329
330	static void __init ksm_slab_free(void)
331	{
332	kmem_cache_destroy(s: mm_slot_cache);
333	kmem_cache_destroy(s: stable_node_cache);
334	kmem_cache_destroy(s: rmap_item_cache);
335	mm_slot_cache = NULL;
336	}
337
338	static __always_inline bool is_stable_node_chain(struct ksm_stable_node *chain)
339	{
340	return chain->rmap_hlist_len == STABLE_NODE_CHAIN;
341	}
342
343	static __always_inline bool is_stable_node_dup(struct ksm_stable_node *dup)
344	{
345	return dup->head == STABLE_NODE_DUP_HEAD;
346	}
347
348	static inline void stable_node_chain_add_dup(struct ksm_stable_node *dup,
349	struct ksm_stable_node *chain)
350	{
351	VM_BUG_ON(is_stable_node_dup(dup));
352	dup->head = STABLE_NODE_DUP_HEAD;
353	VM_BUG_ON(!is_stable_node_chain(chain));
354	hlist_add_head(n: &dup->hlist_dup, h: &chain->hlist);
355	ksm_stable_node_dups++;
356	}
357
358	static inline void __stable_node_dup_del(struct ksm_stable_node *dup)
359	{
360	VM_BUG_ON(!is_stable_node_dup(dup));
361	hlist_del(n: &dup->hlist_dup);
362	ksm_stable_node_dups--;
363	}
364
365	static inline void stable_node_dup_del(struct ksm_stable_node *dup)
366	{
367	VM_BUG_ON(is_stable_node_chain(dup));
368	if (is_stable_node_dup(dup))
369	__stable_node_dup_del(dup);
370	else
371	rb_erase(&dup->node, root_stable_tree + NUMA(dup->nid));
372	#ifdef CONFIG_DEBUG_VM
373	dup->head = NULL;
374	#endif
375	}
376
377	static inline struct ksm_rmap_item *alloc_rmap_item(void)
378	{
379	struct ksm_rmap_item *rmap_item;
380
381	rmap_item = kmem_cache_zalloc(k: rmap_item_cache, GFP_KERNEL |
382	__GFP_NORETRY | __GFP_NOWARN);
383	if (rmap_item)
384	ksm_rmap_items++;
385	return rmap_item;
386	}
387
388	static inline void free_rmap_item(struct ksm_rmap_item *rmap_item)
389	{
390	ksm_rmap_items--;
391	rmap_item->mm->ksm_rmap_items--;
392	rmap_item->mm = NULL; /* debug safety */
393	kmem_cache_free(s: rmap_item_cache, objp: rmap_item);
394	}
395
396	static inline struct ksm_stable_node *alloc_stable_node(void)
397	{
398	/*
399	* The allocation can take too long with GFP_KERNEL when memory is under
400	* pressure, which may lead to hung task warnings. Adding __GFP_HIGH
401	* grants access to memory reserves, helping to avoid this problem.
402	*/
403	return kmem_cache_alloc(cachep: stable_node_cache, GFP_KERNEL | __GFP_HIGH);
404	}
405
406	static inline void free_stable_node(struct ksm_stable_node *stable_node)
407	{
408	VM_BUG_ON(stable_node->rmap_hlist_len &&
409	!is_stable_node_chain(stable_node));
410	kmem_cache_free(s: stable_node_cache, objp: stable_node);
411	}
412
413	/*
414	* ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
415	* page tables after it has passed through ksm_exit() - which, if necessary,
416	* takes mmap_lock briefly to serialize against them. ksm_exit() does not set
417	* a special flag: they can just back out as soon as mm_users goes to zero.
418	* ksm_test_exit() is used throughout to make this test for exit: in some
419	* places for correctness, in some places just to avoid unnecessary work.
420	*/
421	static inline bool ksm_test_exit(struct mm_struct *mm)
422	{
423	return atomic_read(v: &mm->mm_users) == 0;
424	}
425
426	static int break_ksm_pmd_entry(pmd_t *pmd, unsigned long addr, unsigned long next,
427	struct mm_walk *walk)
428	{
429	struct page *page = NULL;
430	spinlock_t *ptl;
431	pte_t *pte;
432	int ret;
433
434	if (pmd_leaf(pte: *pmd) || !pmd_present(pmd: *pmd))
435	return 0;
436
437	pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
438	if (pte_present(a: *pte)) {
439	page = vm_normal_page(vma: walk->vma, addr, pte: *pte);
440	} else if (!pte_none(pte: *pte)) {
441	swp_entry_t entry = pte_to_swp_entry(*pte);
442
443	/*
444	* As KSM pages remain KSM pages until freed, no need to wait
445	* here for migration to end.
446	*/
447	if (is_migration_entry(entry))
448	page = pfn_swap_entry_to_page(entry);
449	}
450	ret = page && PageKsm(page);
451	pte_unmap_unlock(pte, ptl);
452	return ret;
453	}
454
455	static const struct mm_walk_ops break_ksm_ops = {
456	.pmd_entry = break_ksm_pmd_entry,
457	};
458
459	/*
460	* We use break_ksm to break COW on a ksm page by triggering unsharing,
461	* such that the ksm page will get replaced by an exclusive anonymous page.
462	*
463	* We take great care only to touch a ksm page, in a VM_MERGEABLE vma,
464	* in case the application has unmapped and remapped mm,addr meanwhile.
465	* Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP
466	* mmap of /dev/mem, where we would not want to touch it.
467	*
468	* FAULT_FLAG_REMOTE/FOLL_REMOTE are because we do this outside the context
469	* of the process that owns 'vma'. We also do not want to enforce
470	* protection keys here anyway.
471	*/
472	static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
473	{
474	vm_fault_t ret = 0;
475
476	do {
477	int ksm_page;
478
479	cond_resched();
480	ksm_page = walk_page_range_vma(vma, start: addr, end: addr + 1,
481	ops: &break_ksm_ops, NULL);
482	if (WARN_ON_ONCE(ksm_page < 0))
483	return ksm_page;
484	if (!ksm_page)
485	return 0;
486	ret = handle_mm_fault(vma, address: addr,
487	flags: FAULT_FLAG_UNSHARE | FAULT_FLAG_REMOTE,
488	NULL);
489	} while (!(ret & (VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV | VM_FAULT_OOM)));
490	/*
491	* We must loop until we no longer find a KSM page because
492	* handle_mm_fault() may back out if there's any difficulty e.g. if
493	* pte accessed bit gets updated concurrently.
494	*
495	* VM_FAULT_SIGBUS could occur if we race with truncation of the
496	* backing file, which also invalidates anonymous pages: that's
497	* okay, that truncation will have unmapped the PageKsm for us.
498	*
499	* VM_FAULT_OOM: at the time of writing (late July 2009), setting
500	* aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
501	* current task has TIF_MEMDIE set, and will be OOM killed on return
502	* to user; and ksmd, having no mm, would never be chosen for that.
503	*
504	* But if the mm is in a limited mem_cgroup, then the fault may fail
505	* with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
506	* even ksmd can fail in this way - though it's usually breaking ksm
507	* just to undo a merge it made a moment before, so unlikely to oom.
508	*
509	* That's a pity: we might therefore have more kernel pages allocated
510	* than we're counting as nodes in the stable tree; but ksm_do_scan
511	* will retry to break_cow on each pass, so should recover the page
512	* in due course. The important thing is to not let VM_MERGEABLE
513	* be cleared while any such pages might remain in the area.
514	*/
515	return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
516	}
517
518	static bool vma_ksm_compatible(struct vm_area_struct *vma)
519	{
520	if (vma->vm_flags & (VM_SHARED | VM_MAYSHARE | VM_PFNMAP |
521	VM_IO | VM_DONTEXPAND | VM_HUGETLB |
522	VM_MIXEDMAP))
523	return false; /* just ignore the advice */
524
525	if (vma_is_dax(vma))
526	return false;
527
528	#ifdef VM_SAO
529	if (vma->vm_flags & VM_SAO)
530	return false;
531	#endif
532	#ifdef VM_SPARC_ADI
533	if (vma->vm_flags & VM_SPARC_ADI)
534	return false;
535	#endif
536
537	return true;
538	}
539
540	static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm,
541	unsigned long addr)
542	{
543	struct vm_area_struct *vma;
544	if (ksm_test_exit(mm))
545	return NULL;
546	vma = vma_lookup(mm, addr);
547	if (!vma || !(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
548	return NULL;
549	return vma;
550	}
551
552	static void break_cow(struct ksm_rmap_item *rmap_item)
553	{
554	struct mm_struct *mm = rmap_item->mm;
555	unsigned long addr = rmap_item->address;
556	struct vm_area_struct *vma;
557
558	/*
559	* It is not an accident that whenever we want to break COW
560	* to undo, we also need to drop a reference to the anon_vma.
561	*/
562	put_anon_vma(rmap_item->anon_vma);
563
564	mmap_read_lock(mm);
565	vma = find_mergeable_vma(mm, addr);
566	if (vma)
567	break_ksm(vma, addr);
568	mmap_read_unlock(mm);
569	}
570
571	static struct page *get_mergeable_page(struct ksm_rmap_item *rmap_item)
572	{
573	struct mm_struct *mm = rmap_item->mm;
574	unsigned long addr = rmap_item->address;
575	struct vm_area_struct *vma;
576	struct page *page;
577
578	mmap_read_lock(mm);
579	vma = find_mergeable_vma(mm, addr);
580	if (!vma)
581	goto out;
582
583	page = follow_page(vma, address: addr, foll_flags: FOLL_GET);
584	if (IS_ERR_OR_NULL(ptr: page))
585	goto out;
586	if (is_zone_device_page(page))
587	goto out_putpage;
588	if (PageAnon(page)) {
589	flush_anon_page(vma, page, vmaddr: addr);
590	flush_dcache_page(page);
591	} else {
592	out_putpage:
593	put_page(page);
594	out:
595	page = NULL;
596	}
597	mmap_read_unlock(mm);
598	return page;
599	}
600
601	/*
602	* This helper is used for getting right index into array of tree roots.
603	* When merge_across_nodes knob is set to 1, there are only two rb-trees for
604	* stable and unstable pages from all nodes with roots in index 0. Otherwise,
605	* every node has its own stable and unstable tree.
606	*/
607	static inline int get_kpfn_nid(unsigned long kpfn)
608	{
609	return ksm_merge_across_nodes ? 0 : NUMA(pfn_to_nid(kpfn));
610	}
611
612	static struct ksm_stable_node *alloc_stable_node_chain(struct ksm_stable_node *dup,
613	struct rb_root *root)
614	{
615	struct ksm_stable_node *chain = alloc_stable_node();
616	VM_BUG_ON(is_stable_node_chain(dup));
617	if (likely(chain)) {
618	INIT_HLIST_HEAD(&chain->hlist);
619	chain->chain_prune_time = jiffies;
620	chain->rmap_hlist_len = STABLE_NODE_CHAIN;
621	#if defined (CONFIG_DEBUG_VM) && defined(CONFIG_NUMA)
622	chain->nid = NUMA_NO_NODE; /* debug */
623	#endif
624	ksm_stable_node_chains++;
625
626	/*
627	* Put the stable node chain in the first dimension of
628	* the stable tree and at the same time remove the old
629	* stable node.
630	*/
631	rb_replace_node(victim: &dup->node, new: &chain->node, root);
632
633	/*
634	* Move the old stable node to the second dimension
635	* queued in the hlist_dup. The invariant is that all
636	* dup stable_nodes in the chain->hlist point to pages
637	* that are write protected and have the exact same
638	* content.
639	*/
640	stable_node_chain_add_dup(dup, chain);
641	}
642	return chain;
643	}
644
645	static inline void free_stable_node_chain(struct ksm_stable_node *chain,
646	struct rb_root *root)
647	{
648	rb_erase(&chain->node, root);
649	free_stable_node(stable_node: chain);
650	ksm_stable_node_chains--;
651	}
652
653	static void remove_node_from_stable_tree(struct ksm_stable_node *stable_node)
654	{
655	struct ksm_rmap_item *rmap_item;
656
657	/* check it's not STABLE_NODE_CHAIN or negative */
658	BUG_ON(stable_node->rmap_hlist_len < 0);
659
660	hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
661	if (rmap_item->hlist.next) {
662	ksm_pages_sharing--;
663	trace_ksm_remove_rmap_item(pfn: stable_node->kpfn, rmap_item, mm: rmap_item->mm);
664	} else {
665	ksm_pages_shared--;
666	}
667
668	rmap_item->mm->ksm_merging_pages--;
669
670	VM_BUG_ON(stable_node->rmap_hlist_len <= 0);
671	stable_node->rmap_hlist_len--;
672	put_anon_vma(rmap_item->anon_vma);
673	rmap_item->address &= PAGE_MASK;
674	cond_resched();
675	}
676
677	/*
678	* We need the second aligned pointer of the migrate_nodes
679	* list_head to stay clear from the rb_parent_color union
680	* (aligned and different than any node) and also different
681	* from &migrate_nodes. This will verify that future list.h changes
682	* don't break STABLE_NODE_DUP_HEAD. Only recent gcc can handle it.
683	*/
684	BUILD_BUG_ON(STABLE_NODE_DUP_HEAD <= &migrate_nodes);
685	BUILD_BUG_ON(STABLE_NODE_DUP_HEAD >= &migrate_nodes + 1);
686
687	trace_ksm_remove_ksm_page(pfn: stable_node->kpfn);
688	if (stable_node->head == &migrate_nodes)
689	list_del(entry: &stable_node->list);
690	else
691	stable_node_dup_del(dup: stable_node);
692	free_stable_node(stable_node);
693	}
694
695	enum get_ksm_page_flags {
696	GET_KSM_PAGE_NOLOCK,
697	GET_KSM_PAGE_LOCK,
698	GET_KSM_PAGE_TRYLOCK
699	};
700
701	/*
702	* get_ksm_page: checks if the page indicated by the stable node
703	* is still its ksm page, despite having held no reference to it.
704	* In which case we can trust the content of the page, and it
705	* returns the gotten page; but if the page has now been zapped,
706	* remove the stale node from the stable tree and return NULL.
707	* But beware, the stable node's page might be being migrated.
708	*
709	* You would expect the stable_node to hold a reference to the ksm page.
710	* But if it increments the page's count, swapping out has to wait for
711	* ksmd to come around again before it can free the page, which may take
712	* seconds or even minutes: much too unresponsive. So instead we use a
713	* "keyhole reference": access to the ksm page from the stable node peeps
714	* out through its keyhole to see if that page still holds the right key,
715	* pointing back to this stable node. This relies on freeing a PageAnon
716	* page to reset its page->mapping to NULL, and relies on no other use of
717	* a page to put something that might look like our key in page->mapping.
718	* is on its way to being freed; but it is an anomaly to bear in mind.
719	*/
720	static struct page *get_ksm_page(struct ksm_stable_node *stable_node,
721	enum get_ksm_page_flags flags)
722	{
723	struct page *page;
724	void *expected_mapping;
725	unsigned long kpfn;
726
727	expected_mapping = (void *)((unsigned long)stable_node |
728	PAGE_MAPPING_KSM);
729	again:
730	kpfn = READ_ONCE(stable_node->kpfn); /* Address dependency. */
731	page = pfn_to_page(kpfn);
732	if (READ_ONCE(page->mapping) != expected_mapping)
733	goto stale;
734
735	/*
736	* We cannot do anything with the page while its refcount is 0.
737	* Usually 0 means free, or tail of a higher-order page: in which
738	* case this node is no longer referenced, and should be freed;
739	* however, it might mean that the page is under page_ref_freeze().
740	* The __remove_mapping() case is easy, again the node is now stale;
741	* the same is in reuse_ksm_page() case; but if page is swapcache
742	* in folio_migrate_mapping(), it might still be our page,
743	* in which case it's essential to keep the node.
744	*/
745	while (!get_page_unless_zero(page)) {
746	/*
747	* Another check for page->mapping != expected_mapping would
748	* work here too. We have chosen the !PageSwapCache test to
749	* optimize the common case, when the page is or is about to
750	* be freed: PageSwapCache is cleared (under spin_lock_irq)
751	* in the ref_freeze section of __remove_mapping(); but Anon
752	* page->mapping reset to NULL later, in free_pages_prepare().
753	*/
754	if (!PageSwapCache(page))
755	goto stale;
756	cpu_relax();
757	}
758
759	if (READ_ONCE(page->mapping) != expected_mapping) {
760	put_page(page);
761	goto stale;
762	}
763
764	if (flags == GET_KSM_PAGE_TRYLOCK) {
765	if (!trylock_page(page)) {
766	put_page(page);
767	return ERR_PTR(-EBUSY);
768	}
769	} else if (flags == GET_KSM_PAGE_LOCK)
770	lock_page(page);
771
772	if (flags != GET_KSM_PAGE_NOLOCK) {
773	if (READ_ONCE(page->mapping) != expected_mapping) {
774	unlock_page(page);
775	put_page(page);
776	goto stale;
777	}
778	}
779	return page;
780
781	stale:
782	/*
783	* We come here from above when page->mapping or !PageSwapCache
784	* suggests that the node is stale; but it might be under migration.
785	* We need smp_rmb(), matching the smp_wmb() in folio_migrate_ksm(),
786	* before checking whether node->kpfn has been changed.
787	*/
788	smp_rmb();
789	if (READ_ONCE(stable_node->kpfn) != kpfn)
790	goto again;
791	remove_node_from_stable_tree(stable_node);
792	return NULL;
793	}
794
795	/*
796	* Removing rmap_item from stable or unstable tree.
797	* This function will clean the information from the stable/unstable tree.
798	*/
799	static void remove_rmap_item_from_tree(struct ksm_rmap_item *rmap_item)
800	{
801	if (rmap_item->address & STABLE_FLAG) {
802	struct ksm_stable_node *stable_node;
803	struct page *page;
804
805	stable_node = rmap_item->head;
806	page = get_ksm_page(stable_node, flags: GET_KSM_PAGE_LOCK);
807	if (!page)
808	goto out;
809
810	hlist_del(n: &rmap_item->hlist);
811	unlock_page(page);
812	put_page(page);
813
814	if (!hlist_empty(h: &stable_node->hlist))
815	ksm_pages_sharing--;
816	else
817	ksm_pages_shared--;
818
819	rmap_item->mm->ksm_merging_pages--;
820
821	VM_BUG_ON(stable_node->rmap_hlist_len <= 0);
822	stable_node->rmap_hlist_len--;
823
824	put_anon_vma(rmap_item->anon_vma);
825	rmap_item->head = NULL;
826	rmap_item->address &= PAGE_MASK;
827
828	} else if (rmap_item->address & UNSTABLE_FLAG) {
829	unsigned char age;
830	/*
831	* Usually ksmd can and must skip the rb_erase, because
832	* root_unstable_tree was already reset to RB_ROOT.
833	* But be careful when an mm is exiting: do the rb_erase
834	* if this rmap_item was inserted by this scan, rather
835	* than left over from before.
836	*/
837	age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
838	BUG_ON(age > 1);
839	if (!age)
840	rb_erase(&rmap_item->node,
841	root_unstable_tree + NUMA(rmap_item->nid));
842	ksm_pages_unshared--;
843	rmap_item->address &= PAGE_MASK;
844	}
845	out:
846	cond_resched(); /* we're called from many long loops */
847	}
848
849	static void remove_trailing_rmap_items(struct ksm_rmap_item **rmap_list)
850	{
851	while (*rmap_list) {
852	struct ksm_rmap_item *rmap_item = *rmap_list;
853	*rmap_list = rmap_item->rmap_list;
854	remove_rmap_item_from_tree(rmap_item);
855	free_rmap_item(rmap_item);
856	}
857	}
858
859	/*
860	* Though it's very tempting to unmerge rmap_items from stable tree rather
861	* than check every pte of a given vma, the locking doesn't quite work for
862	* that - an rmap_item is assigned to the stable tree after inserting ksm
863	* page and upping mmap_lock. Nor does it fit with the way we skip dup'ing
864	* rmap_items from parent to child at fork time (so as not to waste time
865	* if exit comes before the next scan reaches it).
866	*
867	* Similarly, although we'd like to remove rmap_items (so updating counts
868	* and freeing memory) when unmerging an area, it's easier to leave that
869	* to the next pass of ksmd - consider, for example, how ksmd might be
870	* in cmp_and_merge_page on one of the rmap_items we would be removing.
871	*/
872	static int unmerge_ksm_pages(struct vm_area_struct *vma,
873	unsigned long start, unsigned long end)
874	{
875	unsigned long addr;
876	int err = 0;
877
878	for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
879	if (ksm_test_exit(mm: vma->vm_mm))
880	break;
881	if (signal_pending(current))
882	err = -ERESTARTSYS;
883	else
884	err = break_ksm(vma, addr);
885	}
886	return err;
887	}
888
889	static inline struct ksm_stable_node *folio_stable_node(struct folio *folio)
890	{
891	return folio_test_ksm(folio) ? folio_raw_mapping(folio) : NULL;
892	}
893
894	static inline struct ksm_stable_node *page_stable_node(struct page *page)
895	{
896	return folio_stable_node(page_folio(page));
897	}
898
899	static inline void set_page_stable_node(struct page *page,
900	struct ksm_stable_node *stable_node)
901	{
902	VM_BUG_ON_PAGE(PageAnon(page) && PageAnonExclusive(page), page);
903	page->mapping = (void *)((unsigned long)stable_node | PAGE_MAPPING_KSM);
904	}
905
906	#ifdef CONFIG_SYSFS
907	/*
908	* Only called through the sysfs control interface:
909	*/
910	static int remove_stable_node(struct ksm_stable_node *stable_node)
911	{
912	struct page *page;
913	int err;
914
915	page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK);
916	if (!page) {
917	/*
918	* get_ksm_page did remove_node_from_stable_tree itself.
919	*/
920	return 0;
921	}
922
923	/*
924	* Page could be still mapped if this races with __mmput() running in
925	* between ksm_exit() and exit_mmap(). Just refuse to let
926	* merge_across_nodes/max_page_sharing be switched.
927	*/
928	err = -EBUSY;
929	if (!page_mapped(page)) {
930	/*
931	* The stable node did not yet appear stale to get_ksm_page(),
932	* since that allows for an unmapped ksm page to be recognized
933	* right up until it is freed; but the node is safe to remove.
934	* This page might be in a pagevec waiting to be freed,
935	* or it might be PageSwapCache (perhaps under writeback),
936	* or it might have been removed from swapcache a moment ago.
937	*/
938	set_page_stable_node(page, NULL);
939	remove_node_from_stable_tree(stable_node);
940	err = 0;
941	}
942
943	unlock_page(page);
944	put_page(page);
945	return err;
946	}
947
948	static int remove_stable_node_chain(struct ksm_stable_node *stable_node,
949	struct rb_root *root)
950	{
951	struct ksm_stable_node *dup;
952	struct hlist_node *hlist_safe;
953
954	if (!is_stable_node_chain(stable_node)) {
955	VM_BUG_ON(is_stable_node_dup(stable_node));
956	if (remove_stable_node(stable_node))
957	return true;
958	else
959	return false;
960	}
961
962	hlist_for_each_entry_safe(dup, hlist_safe,
963	&stable_node->hlist, hlist_dup) {
964	VM_BUG_ON(!is_stable_node_dup(dup));
965	if (remove_stable_node(dup))
966	return true;
967	}
968	BUG_ON(!hlist_empty(&stable_node->hlist));
969	free_stable_node_chain(stable_node, root);
970	return false;
971	}
972
973	static int remove_all_stable_nodes(void)
974	{
975	struct ksm_stable_node *stable_node, *next;
976	int nid;
977	int err = 0;
978
979	for (nid = 0; nid < ksm_nr_node_ids; nid++) {
980	while (root_stable_tree[nid].rb_node) {
981	stable_node = rb_entry(root_stable_tree[nid].rb_node,
982	struct ksm_stable_node, node);
983	if (remove_stable_node_chain(stable_node,
984	root_stable_tree + nid)) {
985	err = -EBUSY;
986	break; /* proceed to next nid */
987	}
988	cond_resched();
989	}
990	}
991	list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) {
992	if (remove_stable_node(stable_node))
993	err = -EBUSY;
994	cond_resched();
995	}
996	return err;
997	}
998
999	static int unmerge_and_remove_all_rmap_items(void)
1000	{
1001	struct ksm_mm_slot *mm_slot;
1002	struct mm_slot *slot;
1003	struct mm_struct *mm;
1004	struct vm_area_struct *vma;
1005	int err = 0;
1006
1007	spin_lock(&ksm_mmlist_lock);
1008	slot = list_entry(ksm_mm_head.slot.mm_node.next,
1009	struct mm_slot, mm_node);
1010	ksm_scan.mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot);
1011	spin_unlock(&ksm_mmlist_lock);
1012
1013	for (mm_slot = ksm_scan.mm_slot; mm_slot != &ksm_mm_head;
1014	mm_slot = ksm_scan.mm_slot) {
1015	VMA_ITERATOR(vmi, mm_slot->slot.mm, 0);
1016
1017	mm = mm_slot->slot.mm;
1018	mmap_read_lock(mm);
1019
1020	/*
1021	* Exit right away if mm is exiting to avoid lockdep issue in
1022	* the maple tree
1023	*/
1024	if (ksm_test_exit(mm))
1025	goto mm_exiting;
1026
1027	for_each_vma(vmi, vma) {
1028	if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
1029	continue;
1030	err = unmerge_ksm_pages(vma,
1031	vma->vm_start, vma->vm_end);
1032	if (err)
1033	goto error;
1034	}
1035
1036	mm_exiting:
1037	remove_trailing_rmap_items(&mm_slot->rmap_list);
1038	mmap_read_unlock(mm);
1039
1040	spin_lock(&ksm_mmlist_lock);
1041	slot = list_entry(mm_slot->slot.mm_node.next,
1042	struct mm_slot, mm_node);
1043	ksm_scan.mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot);
1044	if (ksm_test_exit(mm)) {
1045	hash_del(&mm_slot->slot.hash);
1046	list_del(&mm_slot->slot.mm_node);
1047	spin_unlock(&ksm_mmlist_lock);
1048
1049	mm_slot_free(mm_slot_cache, mm_slot);
1050	clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1051	clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
1052	mmdrop(mm);
1053	} else
1054	spin_unlock(&ksm_mmlist_lock);
1055	}
1056
1057	/* Clean up stable nodes, but don't worry if some are still busy */
1058	remove_all_stable_nodes();
1059	ksm_scan.seqnr = 0;
1060	return 0;
1061
1062	error:
1063	mmap_read_unlock(mm);
1064	spin_lock(&ksm_mmlist_lock);
1065	ksm_scan.mm_slot = &ksm_mm_head;
1066	spin_unlock(&ksm_mmlist_lock);
1067	return err;
1068	}
1069	#endif /* CONFIG_SYSFS */
1070
1071	static u32 calc_checksum(struct page *page)
1072	{
1073	u32 checksum;
1074	void *addr = kmap_atomic(page);
1075	checksum = xxhash(input: addr, PAGE_SIZE, seed: 0);
1076	kunmap_atomic(addr);
1077	return checksum;
1078	}
1079
1080	static int write_protect_page(struct vm_area_struct *vma, struct page *page,
1081	pte_t *orig_pte)
1082	{
1083	struct mm_struct *mm = vma->vm_mm;
1084	DEFINE_PAGE_VMA_WALK(pvmw, page, vma, 0, 0);
1085	int swapped;
1086	int err = -EFAULT;
1087	struct mmu_notifier_range range;
1088	bool anon_exclusive;
1089
1090	pvmw.address = page_address_in_vma(page, vma);
1091	if (pvmw.address == -EFAULT)
1092	goto out;
1093
1094	BUG_ON(PageTransCompound(page));
1095
1096	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm, pvmw.address,
1097	pvmw.address + PAGE_SIZE);
1098	mmu_notifier_invalidate_range_start(range: &range);
1099
1100	if (!page_vma_mapped_walk(&pvmw))
1101	goto out_mn;
1102	if (WARN_ONCE(!pvmw.pte, "Unexpected PMD mapping?"))
1103	goto out_unlock;
1104
1105	anon_exclusive = PageAnonExclusive(page);
1106	if (pte_write(*pvmw.pte) || pte_dirty(*pvmw.pte) ||
1107	anon_exclusive || mm_tlb_flush_pending(mm)) {
1108	pte_t entry;
1109
1110	swapped = PageSwapCache(page);
1111	flush_cache_page(vma, pvmw.address, page_to_pfn(page));
1112	/*
1113	* Ok this is tricky, when get_user_pages_fast() run it doesn't
1114	* take any lock, therefore the check that we are going to make
1115	* with the pagecount against the mapcount is racy and
1116	* O_DIRECT can happen right after the check.
1117	* So we clear the pte and flush the tlb before the check
1118	* this assure us that no O_DIRECT can happen after the check
1119	* or in the middle of the check.
1120	*
1121	* No need to notify as we are downgrading page table to read
1122	* only not changing it to point to a new page.
1123	*
1124	* See Documentation/mm/mmu_notifier.rst
1125	*/
1126	entry = ptep_clear_flush(vma, pvmw.address, pvmw.pte);
1127	/*
1128	* Check that no O_DIRECT or similar I/O is in progress on the
1129	* page
1130	*/
1131	if (page_mapcount(page) + 1 + swapped != page_count(page)) {
1132	set_pte_at(mm, pvmw.address, pvmw.pte, entry);
1133	goto out_unlock;
1134	}
1135
1136	/* See page_try_share_anon_rmap(): clear PTE first. */
1137	if (anon_exclusive && page_try_share_anon_rmap(page)) {
1138	set_pte_at(mm, pvmw.address, pvmw.pte, entry);
1139	goto out_unlock;
1140	}
1141
1142	if (pte_dirty(pte: entry))
1143	set_page_dirty(page);
1144	entry = pte_mkclean(pte: entry);
1145
1146	if (pte_write(pte: entry))
1147	entry = pte_wrprotect(pte: entry);
1148
1149	set_pte_at_notify(mm, pvmw.address, pvmw.pte, entry);
1150	}
1151	*orig_pte = *pvmw.pte;
1152	err = 0;
1153
1154	out_unlock:
1155	page_vma_mapped_walk_done(&pvmw);
1156	out_mn:
1157	mmu_notifier_invalidate_range_end(range: &range);
1158	out:
1159	return err;
1160	}
1161
1162	/**
1163	* replace_page - replace page in vma by new ksm page
1164	* @vma: vma that holds the pte pointing to page
1165	* @page: the page we are replacing by kpage
1166	* @kpage: the ksm page we replace page by
1167	* @orig_pte: the original value of the pte
1168	*
1169	* Returns 0 on success, -EFAULT on failure.
1170	*/
1171	static int replace_page(struct vm_area_struct *vma, struct page *page,
1172	struct page *kpage, pte_t orig_pte)
1173	{
1174	struct mm_struct *mm = vma->vm_mm;
1175	struct folio *folio;
1176	pmd_t *pmd;
1177	pmd_t pmde;
1178	pte_t *ptep;
1179	pte_t newpte;
1180	spinlock_t *ptl;
1181	unsigned long addr;
1182	int err = -EFAULT;
1183	struct mmu_notifier_range range;
1184
1185	addr = page_address_in_vma(page, vma);
1186	if (addr == -EFAULT)
1187	goto out;
1188
1189	pmd = mm_find_pmd(mm, address: addr);
1190	if (!pmd)
1191	goto out;
1192	/*
1193	* Some THP functions use the sequence pmdp_huge_clear_flush(), set_pmd_at()
1194	* without holding anon_vma lock for write. So when looking for a
1195	* genuine pmde (in which to find pte), test present and !THP together.
1196	*/
1197	pmde = *pmd;
1198	barrier();
1199	if (!pmd_present(pmd: pmde) || pmd_trans_huge(pmde))
1200	goto out;
1201
1202	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm, addr,
1203	addr + PAGE_SIZE);
1204	mmu_notifier_invalidate_range_start(range: &range);
1205
1206	ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
1207	if (!pte_same(a: *ptep, b: orig_pte)) {
1208	pte_unmap_unlock(ptep, ptl);
1209	goto out_mn;
1210	}
1211	VM_BUG_ON_PAGE(PageAnonExclusive(page), page);
1212	VM_BUG_ON_PAGE(PageAnon(kpage) && PageAnonExclusive(kpage), kpage);
1213
1214	/*
1215	* No need to check ksm_use_zero_pages here: we can only have a
1216	* zero_page here if ksm_use_zero_pages was enabled already.
1217	*/
1218	if (!is_zero_pfn(page_to_pfn(kpage))) {
1219	get_page(page: kpage);
1220	page_add_anon_rmap(kpage, vma, addr, RMAP_NONE);
1221	newpte = mk_pte(kpage, vma->vm_page_prot);
1222	} else {
1223	newpte = pte_mkspecial(pfn_pte(page_to_pfn(kpage),
1224	vma->vm_page_prot));
1225	/*
1226	* We're replacing an anonymous page with a zero page, which is
1227	* not anonymous. We need to do proper accounting otherwise we
1228	* will get wrong values in /proc, and a BUG message in dmesg
1229	* when tearing down the mm.
1230	*/
1231	dec_mm_counter(mm, member: MM_ANONPAGES);
1232	}
1233
1234	flush_cache_page(vma, vmaddr: addr, pfn: pte_pfn(pte: *ptep));
1235	/*
1236	* No need to notify as we are replacing a read only page with another
1237	* read only page with the same content.
1238	*
1239	* See Documentation/mm/mmu_notifier.rst
1240	*/
1241	ptep_clear_flush(vma, addr, ptep);
1242	set_pte_at_notify(mm, addr, ptep, pte: newpte);
1243
1244	folio = page_folio(page);
1245	page_remove_rmap(page, vma, false);
1246	if (!folio_mapped(folio))
1247	folio_free_swap(folio);
1248	folio_put(folio);
1249
1250	pte_unmap_unlock(ptep, ptl);
1251	err = 0;
1252	out_mn:
1253	mmu_notifier_invalidate_range_end(range: &range);
1254	out:
1255	return err;
1256	}
1257
1258	/*
1259	* try_to_merge_one_page - take two pages and merge them into one
1260	* @vma: the vma that holds the pte pointing to page
1261	* @page: the PageAnon page that we want to replace with kpage
1262	* @kpage: the PageKsm page that we want to map instead of page,
1263	* or NULL the first time when we want to use page as kpage.
1264	*
1265	* This function returns 0 if the pages were merged, -EFAULT otherwise.
1266	*/
1267	static int try_to_merge_one_page(struct vm_area_struct *vma,
1268	struct page *page, struct page *kpage)
1269	{
1270	pte_t orig_pte = __pte(0);
1271	int err = -EFAULT;
1272
1273	if (page == kpage) /* ksm page forked */
1274	return 0;
1275
1276	if (!PageAnon(page))
1277	goto out;
1278
1279	/*
1280	* We need the page lock to read a stable PageSwapCache in
1281	* write_protect_page(). We use trylock_page() instead of
1282	* lock_page() because we don't want to wait here - we
1283	* prefer to continue scanning and merging different pages,
1284	* then come back to this page when it is unlocked.
1285	*/
1286	if (!trylock_page(page))
1287	goto out;
1288
1289	if (PageTransCompound(page)) {
1290	if (split_huge_page(page))
1291	goto out_unlock;
1292	}
1293
1294	/*
1295	* If this anonymous page is mapped only here, its pte may need
1296	* to be write-protected. If it's mapped elsewhere, all of its
1297	* ptes are necessarily already write-protected. But in either
1298	* case, we need to lock and check page_count is not raised.
1299	*/
1300	if (write_protect_page(vma, page, orig_pte: &orig_pte) == 0) {
1301	if (!kpage) {
1302	/*
1303	* While we hold page lock, upgrade page from
1304	* PageAnon+anon_vma to PageKsm+NULL stable_node:
1305	* stable_tree_insert() will update stable_node.
1306	*/
1307	set_page_stable_node(page, NULL);
1308	mark_page_accessed(page);
1309	/*
1310	* Page reclaim just frees a clean page with no dirty
1311	* ptes: make sure that the ksm page would be swapped.
1312	*/
1313	if (!PageDirty(page))
1314	SetPageDirty(page);
1315	err = 0;
1316	} else if (pages_identical(page1: page, page2: kpage))
1317	err = replace_page(vma, page, kpage, orig_pte);
1318	}
1319
1320	out_unlock:
1321	unlock_page(page);
1322	out:
1323	return err;
1324	}
1325
1326	/*
1327	* try_to_merge_with_ksm_page - like try_to_merge_two_pages,
1328	* but no new kernel page is allocated: kpage must already be a ksm page.
1329	*
1330	* This function returns 0 if the pages were merged, -EFAULT otherwise.
1331	*/
1332	static int try_to_merge_with_ksm_page(struct ksm_rmap_item *rmap_item,
1333	struct page *page, struct page *kpage)
1334	{
1335	struct mm_struct *mm = rmap_item->mm;
1336	struct vm_area_struct *vma;
1337	int err = -EFAULT;
1338
1339	mmap_read_lock(mm);
1340	vma = find_mergeable_vma(mm, addr: rmap_item->address);
1341	if (!vma)
1342	goto out;
1343
1344	err = try_to_merge_one_page(vma, page, kpage);
1345	if (err)
1346	goto out;
1347
1348	/* Unstable nid is in union with stable anon_vma: remove first */
1349	remove_rmap_item_from_tree(rmap_item);
1350
1351	/* Must get reference to anon_vma while still holding mmap_lock */
1352	rmap_item->anon_vma = vma->anon_vma;
1353	get_anon_vma(vma->anon_vma);
1354	out:
1355	mmap_read_unlock(mm);
1356	trace_ksm_merge_with_ksm_page(ksm_page: kpage, page_to_pfn(kpage ? kpage : page),
1357	rmap_item, mm, err);
1358	return err;
1359	}
1360
1361	/*
1362	* try_to_merge_two_pages - take two identical pages and prepare them
1363	* to be merged into one page.
1364	*
1365	* This function returns the kpage if we successfully merged two identical
1366	* pages into one ksm page, NULL otherwise.
1367	*
1368	* Note that this function upgrades page to ksm page: if one of the pages
1369	* is already a ksm page, try_to_merge_with_ksm_page should be used.
1370	*/
1371	static struct page *try_to_merge_two_pages(struct ksm_rmap_item *rmap_item,
1372	struct page *page,
1373	struct ksm_rmap_item *tree_rmap_item,
1374	struct page *tree_page)
1375	{
1376	int err;
1377
1378	err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
1379	if (!err) {
1380	err = try_to_merge_with_ksm_page(rmap_item: tree_rmap_item,
1381	page: tree_page, kpage: page);
1382	/*
1383	* If that fails, we have a ksm page with only one pte
1384	* pointing to it: so break it.
1385	*/
1386	if (err)
1387	break_cow(rmap_item);
1388	}
1389	return err ? NULL : page;
1390	}
1391
1392	static __always_inline
1393	bool __is_page_sharing_candidate(struct ksm_stable_node *stable_node, int offset)
1394	{
1395	VM_BUG_ON(stable_node->rmap_hlist_len < 0);
1396	/*
1397	* Check that at least one mapping still exists, otherwise
1398	* there's no much point to merge and share with this
1399	* stable_node, as the underlying tree_page of the other
1400	* sharer is going to be freed soon.
1401	*/
1402	return stable_node->rmap_hlist_len &&
1403	stable_node->rmap_hlist_len + offset < ksm_max_page_sharing;
1404	}
1405
1406	static __always_inline
1407	bool is_page_sharing_candidate(struct ksm_stable_node *stable_node)
1408	{
1409	return __is_page_sharing_candidate(stable_node, offset: 0);
1410	}
1411
1412	static struct page *stable_node_dup(struct ksm_stable_node **_stable_node_dup,
1413	struct ksm_stable_node **_stable_node,
1414	struct rb_root *root,
1415	bool prune_stale_stable_nodes)
1416	{
1417	struct ksm_stable_node *dup, *found = NULL, *stable_node = *_stable_node;
1418	struct hlist_node *hlist_safe;
1419	struct page *_tree_page, *tree_page = NULL;
1420	int nr = 0;
1421	int found_rmap_hlist_len;
1422
1423	if (!prune_stale_stable_nodes ||
1424	time_before(jiffies, stable_node->chain_prune_time +
1425	msecs_to_jiffies(
1426	ksm_stable_node_chains_prune_millisecs)))
1427	prune_stale_stable_nodes = false;
1428	else
1429	stable_node->chain_prune_time = jiffies;
1430
1431	hlist_for_each_entry_safe(dup, hlist_safe,
1432	&stable_node->hlist, hlist_dup) {
1433	cond_resched();
1434	/*
1435	* We must walk all stable_node_dup to prune the stale
1436	* stable nodes during lookup.
1437	*
1438	* get_ksm_page can drop the nodes from the
1439	* stable_node->hlist if they point to freed pages
1440	* (that's why we do a _safe walk). The "dup"
1441	* stable_node parameter itself will be freed from
1442	* under us if it returns NULL.
1443	*/
1444	_tree_page = get_ksm_page(stable_node: dup, flags: GET_KSM_PAGE_NOLOCK);
1445	if (!_tree_page)
1446	continue;
1447	nr += 1;
1448	if (is_page_sharing_candidate(stable_node: dup)) {
1449	if (!found ||
1450	dup->rmap_hlist_len > found_rmap_hlist_len) {
1451	if (found)
1452	put_page(page: tree_page);
1453	found = dup;
1454	found_rmap_hlist_len = found->rmap_hlist_len;
1455	tree_page = _tree_page;
1456
1457	/* skip put_page for found dup */
1458	if (!prune_stale_stable_nodes)
1459	break;
1460	continue;
1461	}
1462	}
1463	put_page(page: _tree_page);
1464	}
1465
1466	if (found) {
1467	/*
1468	* nr is counting all dups in the chain only if
1469	* prune_stale_stable_nodes is true, otherwise we may
1470	* break the loop at nr == 1 even if there are
1471	* multiple entries.
1472	*/
1473	if (prune_stale_stable_nodes && nr == 1) {
1474	/*
1475	* If there's not just one entry it would
1476	* corrupt memory, better BUG_ON. In KSM
1477	* context with no lock held it's not even
1478	* fatal.
1479	*/
1480	BUG_ON(stable_node->hlist.first->next);
1481
1482	/*
1483	* There's just one entry and it is below the
1484	* deduplication limit so drop the chain.
1485	*/
1486	rb_replace_node(victim: &stable_node->node, new: &found->node,
1487	root);
1488	free_stable_node(stable_node);
1489	ksm_stable_node_chains--;
1490	ksm_stable_node_dups--;
1491	/*
1492	* NOTE: the caller depends on the stable_node
1493	* to be equal to stable_node_dup if the chain
1494	* was collapsed.
1495	*/
1496	*_stable_node = found;
1497	/*
1498	* Just for robustness, as stable_node is
1499	* otherwise left as a stable pointer, the
1500	* compiler shall optimize it away at build
1501	* time.
1502	*/
1503	stable_node = NULL;
1504	} else if (stable_node->hlist.first != &found->hlist_dup &&
1505	__is_page_sharing_candidate(stable_node: found, offset: 1)) {
1506	/*
1507	* If the found stable_node dup can accept one
1508	* more future merge (in addition to the one
1509	* that is underway) and is not at the head of
1510	* the chain, put it there so next search will
1511	* be quicker in the !prune_stale_stable_nodes
1512	* case.
1513	*
1514	* NOTE: it would be inaccurate to use nr > 1
1515	* instead of checking the hlist.first pointer
1516	* directly, because in the
1517	* prune_stale_stable_nodes case "nr" isn't
1518	* the position of the found dup in the chain,
1519	* but the total number of dups in the chain.
1520	*/
1521	hlist_del(n: &found->hlist_dup);
1522	hlist_add_head(n: &found->hlist_dup,
1523	h: &stable_node->hlist);
1524	}
1525	}
1526
1527	*_stable_node_dup = found;
1528	return tree_page;
1529	}
1530
1531	static struct ksm_stable_node *stable_node_dup_any(struct ksm_stable_node *stable_node,
1532	struct rb_root *root)
1533	{
1534	if (!is_stable_node_chain(chain: stable_node))
1535	return stable_node;
1536	if (hlist_empty(h: &stable_node->hlist)) {
1537	free_stable_node_chain(chain: stable_node, root);
1538	return NULL;
1539	}
1540	return hlist_entry(stable_node->hlist.first,
1541	typeof(*stable_node), hlist_dup);
1542	}
1543
1544	/*
1545	* Like for get_ksm_page, this function can free the *_stable_node and
1546	* *_stable_node_dup if the returned tree_page is NULL.
1547	*
1548	* It can also free and overwrite *_stable_node with the found
1549	* stable_node_dup if the chain is collapsed (in which case
1550	* *_stable_node will be equal to *_stable_node_dup like if the chain
1551	* never existed). It's up to the caller to verify tree_page is not
1552	* NULL before dereferencing *_stable_node or *_stable_node_dup.
1553	*
1554	* *_stable_node_dup is really a second output parameter of this
1555	* function and will be overwritten in all cases, the caller doesn't
1556	* need to initialize it.
1557	*/
1558	static struct page *__stable_node_chain(struct ksm_stable_node **_stable_node_dup,
1559	struct ksm_stable_node **_stable_node,
1560	struct rb_root *root,
1561	bool prune_stale_stable_nodes)
1562	{
1563	struct ksm_stable_node *stable_node = *_stable_node;
1564	if (!is_stable_node_chain(chain: stable_node)) {
1565	if (is_page_sharing_candidate(stable_node)) {
1566	*_stable_node_dup = stable_node;
1567	return get_ksm_page(stable_node, flags: GET_KSM_PAGE_NOLOCK);
1568	}
1569	/*
1570	* _stable_node_dup set to NULL means the stable_node
1571	* reached the ksm_max_page_sharing limit.
1572	*/
1573	*_stable_node_dup = NULL;
1574	return NULL;
1575	}
1576	return stable_node_dup(_stable_node_dup, _stable_node, root,
1577	prune_stale_stable_nodes);
1578	}
1579
1580	static __always_inline struct page *chain_prune(struct ksm_stable_node **s_n_d,
1581	struct ksm_stable_node **s_n,
1582	struct rb_root *root)
1583	{
1584	return __stable_node_chain(stable_node_dup: s_n_d, stable_node: s_n, root, prune_stale_stable_nodes: true);
1585	}
1586
1587	static __always_inline struct page *chain(struct ksm_stable_node **s_n_d,
1588	struct ksm_stable_node *s_n,
1589	struct rb_root *root)
1590	{
1591	struct ksm_stable_node *old_stable_node = s_n;
1592	struct page *tree_page;
1593
1594	tree_page = __stable_node_chain(stable_node_dup: s_n_d, stable_node: &s_n, root, prune_stale_stable_nodes: false);
1595	/* not pruning dups so s_n cannot have changed */
1596	VM_BUG_ON(s_n != old_stable_node);
1597	return tree_page;
1598	}
1599
1600	/*
1601	* stable_tree_search - search for page inside the stable tree
1602	*
1603	* This function checks if there is a page inside the stable tree
1604	* with identical content to the page that we are scanning right now.
1605	*
1606	* This function returns the stable tree node of identical content if found,
1607	* NULL otherwise.
1608	*/
1609	static struct page *stable_tree_search(struct page *page)
1610	{
1611	int nid;
1612	struct rb_root *root;
1613	struct rb_node **new;
1614	struct rb_node *parent;
1615	struct ksm_stable_node *stable_node, *stable_node_dup, *stable_node_any;
1616	struct ksm_stable_node *page_node;
1617
1618	page_node = page_stable_node(page);
1619	if (page_node && page_node->head != &migrate_nodes) {
1620	/* ksm page forked */
1621	get_page(page);
1622	return page;
1623	}
1624
1625	nid = get_kpfn_nid(page_to_pfn(page));
1626	root = root_stable_tree + nid;
1627	again:
1628	new = &root->rb_node;
1629	parent = NULL;
1630
1631	while (*new) {
1632	struct page *tree_page;
1633	int ret;
1634
1635	cond_resched();
1636	stable_node = rb_entry(*new, struct ksm_stable_node, node);
1637	stable_node_any = NULL;
1638	tree_page = chain_prune(s_n_d: &stable_node_dup, s_n: &stable_node, root);
1639	/*
1640	* NOTE: stable_node may have been freed by
1641	* chain_prune() if the returned stable_node_dup is
1642	* not NULL. stable_node_dup may have been inserted in
1643	* the rbtree instead as a regular stable_node (in
1644	* order to collapse the stable_node chain if a single
1645	* stable_node dup was found in it). In such case the
1646	* stable_node is overwritten by the callee to point
1647	* to the stable_node_dup that was collapsed in the
1648	* stable rbtree and stable_node will be equal to
1649	* stable_node_dup like if the chain never existed.
1650	*/
1651	if (!stable_node_dup) {
1652	/*
1653	* Either all stable_node dups were full in
1654	* this stable_node chain, or this chain was
1655	* empty and should be rb_erased.
1656	*/
1657	stable_node_any = stable_node_dup_any(stable_node,
1658	root);
1659	if (!stable_node_any) {
1660	/* rb_erase just run */
1661	goto again;
1662	}
1663	/*
1664	* Take any of the stable_node dups page of
1665	* this stable_node chain to let the tree walk
1666	* continue. All KSM pages belonging to the
1667	* stable_node dups in a stable_node chain
1668	* have the same content and they're
1669	* write protected at all times. Any will work
1670	* fine to continue the walk.
1671	*/
1672	tree_page = get_ksm_page(stable_node: stable_node_any,
1673	flags: GET_KSM_PAGE_NOLOCK);
1674	}
1675	VM_BUG_ON(!stable_node_dup ^ !!stable_node_any);
1676	if (!tree_page) {
1677	/*
1678	* If we walked over a stale stable_node,
1679	* get_ksm_page() will call rb_erase() and it
1680	* may rebalance the tree from under us. So
1681	* restart the search from scratch. Returning
1682	* NULL would be safe too, but we'd generate
1683	* false negative insertions just because some
1684	* stable_node was stale.
1685	*/
1686	goto again;
1687	}
1688
1689	ret = memcmp_pages(page1: page, page2: tree_page);
1690	put_page(page: tree_page);
1691
1692	parent = *new;
1693	if (ret < 0)
1694	new = &parent->rb_left;
1695	else if (ret > 0)
1696	new = &parent->rb_right;
1697	else {
1698	if (page_node) {
1699	VM_BUG_ON(page_node->head != &migrate_nodes);
1700	/*
1701	* Test if the migrated page should be merged
1702	* into a stable node dup. If the mapcount is
1703	* 1 we can migrate it with another KSM page
1704	* without adding it to the chain.
1705	*/
1706	if (page_mapcount(page) > 1)
1707	goto chain_append;
1708	}
1709
1710	if (!stable_node_dup) {
1711	/*
1712	* If the stable_node is a chain and
1713	* we got a payload match in memcmp
1714	* but we cannot merge the scanned
1715	* page in any of the existing
1716	* stable_node dups because they're
1717	* all full, we need to wait the
1718	* scanned page to find itself a match
1719	* in the unstable tree to create a
1720	* brand new KSM page to add later to
1721	* the dups of this stable_node.
1722	*/
1723	return NULL;
1724	}
1725
1726	/*
1727	* Lock and unlock the stable_node's page (which
1728	* might already have been migrated) so that page
1729	* migration is sure to notice its raised count.
1730	* It would be more elegant to return stable_node
1731	* than kpage, but that involves more changes.
1732	*/
1733	tree_page = get_ksm_page(stable_node: stable_node_dup,
1734	flags: GET_KSM_PAGE_TRYLOCK);
1735
1736	if (PTR_ERR(tree_page) == -EBUSY)
1737	return ERR_PTR(-EBUSY);
1738
1739	if (unlikely(!tree_page))
1740	/*
1741	* The tree may have been rebalanced,
1742	* so re-evaluate parent and new.
1743	*/
1744	goto again;
1745	unlock_page(page: tree_page);
1746
1747	if (get_kpfn_nid(kpfn: stable_node_dup->kpfn) !=
1748	NUMA(stable_node_dup->nid)) {
1749	put_page(page: tree_page);
1750	goto replace;
1751	}
1752	return tree_page;
1753	}
1754	}
1755
1756	if (!page_node)
1757	return NULL;
1758
1759	list_del(entry: &page_node->list);
1760	DO_NUMA(page_node->nid = nid);
1761	rb_link_node(node: &page_node->node, parent, rb_link: new);
1762	rb_insert_color(&page_node->node, root);
1763	out:
1764	if (is_page_sharing_candidate(stable_node: page_node)) {
1765	get_page(page);
1766	return page;
1767	} else
1768	return NULL;
1769
1770	replace:
1771	/*
1772	* If stable_node was a chain and chain_prune collapsed it,
1773	* stable_node has been updated to be the new regular
1774	* stable_node. A collapse of the chain is indistinguishable
1775	* from the case there was no chain in the stable
1776	* rbtree. Otherwise stable_node is the chain and
1777	* stable_node_dup is the dup to replace.
1778	*/
1779	if (stable_node_dup == stable_node) {
1780	VM_BUG_ON(is_stable_node_chain(stable_node_dup));
1781	VM_BUG_ON(is_stable_node_dup(stable_node_dup));
1782	/* there is no chain */
1783	if (page_node) {
1784	VM_BUG_ON(page_node->head != &migrate_nodes);
1785	list_del(entry: &page_node->list);
1786	DO_NUMA(page_node->nid = nid);
1787	rb_replace_node(victim: &stable_node_dup->node,
1788	new: &page_node->node,
1789	root);
1790	if (is_page_sharing_candidate(stable_node: page_node))
1791	get_page(page);
1792	else
1793	page = NULL;
1794	} else {
1795	rb_erase(&stable_node_dup->node, root);
1796	page = NULL;
1797	}
1798	} else {
1799	VM_BUG_ON(!is_stable_node_chain(stable_node));
1800	__stable_node_dup_del(dup: stable_node_dup);
1801	if (page_node) {
1802	VM_BUG_ON(page_node->head != &migrate_nodes);
1803	list_del(entry: &page_node->list);
1804	DO_NUMA(page_node->nid = nid);
1805	stable_node_chain_add_dup(dup: page_node, chain: stable_node);
1806	if (is_page_sharing_candidate(stable_node: page_node))
1807	get_page(page);
1808	else
1809	page = NULL;
1810	} else {
1811	page = NULL;
1812	}
1813	}
1814	stable_node_dup->head = &migrate_nodes;
1815	list_add(new: &stable_node_dup->list, head: stable_node_dup->head);
1816	return page;
1817
1818	chain_append:
1819	/* stable_node_dup could be null if it reached the limit */
1820	if (!stable_node_dup)
1821	stable_node_dup = stable_node_any;
1822	/*
1823	* If stable_node was a chain and chain_prune collapsed it,
1824	* stable_node has been updated to be the new regular
1825	* stable_node. A collapse of the chain is indistinguishable
1826	* from the case there was no chain in the stable
1827	* rbtree. Otherwise stable_node is the chain and
1828	* stable_node_dup is the dup to replace.
1829	*/
1830	if (stable_node_dup == stable_node) {
1831	VM_BUG_ON(is_stable_node_dup(stable_node_dup));
1832	/* chain is missing so create it */
1833	stable_node = alloc_stable_node_chain(dup: stable_node_dup,
1834	root);
1835	if (!stable_node)
1836	return NULL;
1837	}
1838	/*
1839	* Add this stable_node dup that was
1840	* migrated to the stable_node chain
1841	* of the current nid for this page
1842	* content.
1843	*/
1844	VM_BUG_ON(!is_stable_node_dup(stable_node_dup));
1845	VM_BUG_ON(page_node->head != &migrate_nodes);
1846	list_del(entry: &page_node->list);
1847	DO_NUMA(page_node->nid = nid);
1848	stable_node_chain_add_dup(dup: page_node, chain: stable_node);
1849	goto out;
1850	}
1851
1852	/*
1853	* stable_tree_insert - insert stable tree node pointing to new ksm page
1854	* into the stable tree.
1855	*
1856	* This function returns the stable tree node just allocated on success,
1857	* NULL otherwise.
1858	*/
1859	static struct ksm_stable_node *stable_tree_insert(struct page *kpage)
1860	{
1861	int nid;
1862	unsigned long kpfn;
1863	struct rb_root *root;
1864	struct rb_node **new;
1865	struct rb_node *parent;
1866	struct ksm_stable_node *stable_node, *stable_node_dup, *stable_node_any;
1867	bool need_chain = false;
1868
1869	kpfn = page_to_pfn(kpage);
1870	nid = get_kpfn_nid(kpfn);
1871	root = root_stable_tree + nid;
1872	again:
1873	parent = NULL;
1874	new = &root->rb_node;
1875
1876	while (*new) {
1877	struct page *tree_page;
1878	int ret;
1879
1880	cond_resched();
1881	stable_node = rb_entry(*new, struct ksm_stable_node, node);
1882	stable_node_any = NULL;
1883	tree_page = chain(s_n_d: &stable_node_dup, s_n: stable_node, root);
1884	if (!stable_node_dup) {
1885	/*
1886	* Either all stable_node dups were full in
1887	* this stable_node chain, or this chain was
1888	* empty and should be rb_erased.
1889	*/
1890	stable_node_any = stable_node_dup_any(stable_node,
1891	root);
1892	if (!stable_node_any) {
1893	/* rb_erase just run */
1894	goto again;
1895	}
1896	/*
1897	* Take any of the stable_node dups page of
1898	* this stable_node chain to let the tree walk
1899	* continue. All KSM pages belonging to the
1900	* stable_node dups in a stable_node chain
1901	* have the same content and they're
1902	* write protected at all times. Any will work
1903	* fine to continue the walk.
1904	*/
1905	tree_page = get_ksm_page(stable_node: stable_node_any,
1906	flags: GET_KSM_PAGE_NOLOCK);
1907	}
1908	VM_BUG_ON(!stable_node_dup ^ !!stable_node_any);
1909	if (!tree_page) {
1910	/*
1911	* If we walked over a stale stable_node,
1912	* get_ksm_page() will call rb_erase() and it
1913	* may rebalance the tree from under us. So
1914	* restart the search from scratch. Returning
1915	* NULL would be safe too, but we'd generate
1916	* false negative insertions just because some
1917	* stable_node was stale.
1918	*/
1919	goto again;
1920	}
1921
1922	ret = memcmp_pages(page1: kpage, page2: tree_page);
1923	put_page(page: tree_page);
1924
1925	parent = *new;
1926	if (ret < 0)
1927	new = &parent->rb_left;
1928	else if (ret > 0)
1929	new = &parent->rb_right;
1930	else {
1931	need_chain = true;
1932	break;
1933	}
1934	}
1935
1936	stable_node_dup = alloc_stable_node();
1937	if (!stable_node_dup)
1938	return NULL;
1939
1940	INIT_HLIST_HEAD(&stable_node_dup->hlist);
1941	stable_node_dup->kpfn = kpfn;
1942	set_page_stable_node(page: kpage, stable_node: stable_node_dup);
1943	stable_node_dup->rmap_hlist_len = 0;
1944	DO_NUMA(stable_node_dup->nid = nid);
1945	if (!need_chain) {
1946	rb_link_node(node: &stable_node_dup->node, parent, rb_link: new);
1947	rb_insert_color(&stable_node_dup->node, root);
1948	} else {
1949	if (!is_stable_node_chain(chain: stable_node)) {
1950	struct ksm_stable_node *orig = stable_node;
1951	/* chain is missing so create it */
1952	stable_node = alloc_stable_node_chain(dup: orig, root);
1953	if (!stable_node) {
1954	free_stable_node(stable_node: stable_node_dup);
1955	return NULL;
1956	}
1957	}
1958	stable_node_chain_add_dup(dup: stable_node_dup, chain: stable_node);
1959	}
1960
1961	return stable_node_dup;
1962	}
1963
1964	/*
1965	* unstable_tree_search_insert - search for identical page,
1966	* else insert rmap_item into the unstable tree.
1967	*
1968	* This function searches for a page in the unstable tree identical to the
1969	* page currently being scanned; and if no identical page is found in the
1970	* tree, we insert rmap_item as a new object into the unstable tree.
1971	*
1972	* This function returns pointer to rmap_item found to be identical
1973	* to the currently scanned page, NULL otherwise.
1974	*
1975	* This function does both searching and inserting, because they share
1976	* the same walking algorithm in an rbtree.
1977	*/
1978	static
1979	struct ksm_rmap_item *unstable_tree_search_insert(struct ksm_rmap_item *rmap_item,
1980	struct page *page,
1981	struct page **tree_pagep)
1982	{
1983	struct rb_node **new;
1984	struct rb_root *root;
1985	struct rb_node *parent = NULL;
1986	int nid;
1987
1988	nid = get_kpfn_nid(page_to_pfn(page));
1989	root = root_unstable_tree + nid;
1990	new = &root->rb_node;
1991
1992	while (*new) {
1993	struct ksm_rmap_item *tree_rmap_item;
1994	struct page *tree_page;
1995	int ret;
1996
1997	cond_resched();
1998	tree_rmap_item = rb_entry(*new, struct ksm_rmap_item, node);
1999	tree_page = get_mergeable_page(rmap_item: tree_rmap_item);
2000	if (!tree_page)
2001	return NULL;
2002
2003	/*
2004	* Don't substitute a ksm page for a forked page.
2005	*/
2006	if (page == tree_page) {
2007	put_page(page: tree_page);
2008	return NULL;
2009	}
2010
2011	ret = memcmp_pages(page1: page, page2: tree_page);
2012
2013	parent = *new;
2014	if (ret < 0) {
2015	put_page(page: tree_page);
2016	new = &parent->rb_left;
2017	} else if (ret > 0) {
2018	put_page(page: tree_page);
2019	new = &parent->rb_right;
2020	} else if (!ksm_merge_across_nodes &&
2021	page_to_nid(page: tree_page) != nid) {
2022	/*
2023	* If tree_page has been migrated to another NUMA node,
2024	* it will be flushed out and put in the right unstable
2025	* tree next time: only merge with it when across_nodes.
2026	*/
2027	put_page(page: tree_page);
2028	return NULL;
2029	} else {
2030	*tree_pagep = tree_page;
2031	return tree_rmap_item;
2032	}
2033	}
2034
2035	rmap_item->address |= UNSTABLE_FLAG;
2036	rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
2037	DO_NUMA(rmap_item->nid = nid);
2038	rb_link_node(node: &rmap_item->node, parent, rb_link: new);
2039	rb_insert_color(&rmap_item->node, root);
2040
2041	ksm_pages_unshared++;
2042	return NULL;
2043	}
2044
2045	/*
2046	* stable_tree_append - add another rmap_item to the linked list of
2047	* rmap_items hanging off a given node of the stable tree, all sharing
2048	* the same ksm page.
2049	*/
2050	static void stable_tree_append(struct ksm_rmap_item *rmap_item,
2051	struct ksm_stable_node *stable_node,
2052	bool max_page_sharing_bypass)
2053	{
2054	/*
2055	* rmap won't find this mapping if we don't insert the
2056	* rmap_item in the right stable_node
2057	* duplicate. page_migration could break later if rmap breaks,
2058	* so we can as well crash here. We really need to check for
2059	* rmap_hlist_len == STABLE_NODE_CHAIN, but we can as well check
2060	* for other negative values as an underflow if detected here
2061	* for the first time (and not when decreasing rmap_hlist_len)
2062	* would be sign of memory corruption in the stable_node.
2063	*/
2064	BUG_ON(stable_node->rmap_hlist_len < 0);
2065
2066	stable_node->rmap_hlist_len++;
2067	if (!max_page_sharing_bypass)
2068	/* possibly non fatal but unexpected overflow, only warn */
2069	WARN_ON_ONCE(stable_node->rmap_hlist_len >
2070	ksm_max_page_sharing);
2071
2072	rmap_item->head = stable_node;
2073	rmap_item->address |= STABLE_FLAG;
2074	hlist_add_head(n: &rmap_item->hlist, h: &stable_node->hlist);
2075
2076	if (rmap_item->hlist.next)
2077	ksm_pages_sharing++;
2078	else
2079	ksm_pages_shared++;
2080
2081	rmap_item->mm->ksm_merging_pages++;
2082	}
2083
2084	/*
2085	* cmp_and_merge_page - first see if page can be merged into the stable tree;
2086	* if not, compare checksum to previous and if it's the same, see if page can
2087	* be inserted into the unstable tree, or merged with a page already there and
2088	* both transferred to the stable tree.
2089	*
2090	* @page: the page that we are searching identical page to.
2091	* @rmap_item: the reverse mapping into the virtual address of this page
2092	*/
2093	static void cmp_and_merge_page(struct page *page, struct ksm_rmap_item *rmap_item)
2094	{
2095	struct mm_struct *mm = rmap_item->mm;
2096	struct ksm_rmap_item *tree_rmap_item;
2097	struct page *tree_page = NULL;
2098	struct ksm_stable_node *stable_node;
2099	struct page *kpage;
2100	unsigned int checksum;
2101	int err;
2102	bool max_page_sharing_bypass = false;
2103
2104	stable_node = page_stable_node(page);
2105	if (stable_node) {
2106	if (stable_node->head != &migrate_nodes &&
2107	get_kpfn_nid(kpfn: READ_ONCE(stable_node->kpfn)) !=
2108	NUMA(stable_node->nid)) {
2109	stable_node_dup_del(dup: stable_node);
2110	stable_node->head = &migrate_nodes;
2111	list_add(new: &stable_node->list, head: stable_node->head);
2112	}
2113	if (stable_node->head != &migrate_nodes &&
2114	rmap_item->head == stable_node)
2115	return;
2116	/*
2117	* If it's a KSM fork, allow it to go over the sharing limit
2118	* without warnings.
2119	*/
2120	if (!is_page_sharing_candidate(stable_node))
2121	max_page_sharing_bypass = true;
2122	}
2123
2124	/* We first start with searching the page inside the stable tree */
2125	kpage = stable_tree_search(page);
2126	if (kpage == page && rmap_item->head == stable_node) {
2127	put_page(page: kpage);
2128	return;
2129	}
2130
2131	remove_rmap_item_from_tree(rmap_item);
2132
2133	if (kpage) {
2134	if (PTR_ERR(kpage) == -EBUSY)
2135	return;
2136
2137	err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
2138	if (!err) {
2139	/*
2140	* The page was successfully merged:
2141	* add its rmap_item to the stable tree.
2142	*/
2143	lock_page(page: kpage);
2144	stable_tree_append(rmap_item, stable_node: page_stable_node(page: kpage),
2145	max_page_sharing_bypass);
2146	unlock_page(page: kpage);
2147	}
2148	put_page(page: kpage);
2149	return;
2150	}
2151
2152	/*
2153	* If the hash value of the page has changed from the last time
2154	* we calculated it, this page is changing frequently: therefore we
2155	* don't want to insert it in the unstable tree, and we don't want
2156	* to waste our time searching for something identical to it there.
2157	*/
2158	checksum = calc_checksum(page);
2159	if (rmap_item->oldchecksum != checksum) {
2160	rmap_item->oldchecksum = checksum;
2161	return;
2162	}
2163
2164	/*
2165	* Same checksum as an empty page. We attempt to merge it with the
2166	* appropriate zero page if the user enabled this via sysfs.
2167	*/
2168	if (ksm_use_zero_pages && (checksum == zero_checksum)) {
2169	struct vm_area_struct *vma;
2170
2171	mmap_read_lock(mm);
2172	vma = find_mergeable_vma(mm, addr: rmap_item->address);
2173	if (vma) {
2174	err = try_to_merge_one_page(vma, page,
2175	ZERO_PAGE(rmap_item->address));
2176	trace_ksm_merge_one_page(
2177	page_to_pfn(ZERO_PAGE(rmap_item->address)),
2178	rmap_item, mm, err);
2179	} else {
2180	/*
2181	* If the vma is out of date, we do not need to
2182	* continue.
2183	*/
2184	err = 0;
2185	}
2186	mmap_read_unlock(mm);
2187	/*
2188	* In case of failure, the page was not really empty, so we
2189	* need to continue. Otherwise we're done.
2190	*/
2191	if (!err)
2192	return;
2193	}
2194	tree_rmap_item =
2195	unstable_tree_search_insert(rmap_item, page, tree_pagep: &tree_page);
2196	if (tree_rmap_item) {
2197	bool split;
2198
2199	kpage = try_to_merge_two_pages(rmap_item, page,
2200	tree_rmap_item, tree_page);
2201	/*
2202	* If both pages we tried to merge belong to the same compound
2203	* page, then we actually ended up increasing the reference
2204	* count of the same compound page twice, and split_huge_page
2205	* failed.
2206	* Here we set a flag if that happened, and we use it later to
2207	* try split_huge_page again. Since we call put_page right
2208	* afterwards, the reference count will be correct and
2209	* split_huge_page should succeed.
2210	*/
2211	split = PageTransCompound(page)
2212	&& compound_head(page) == compound_head(tree_page);
2213	put_page(page: tree_page);
2214	if (kpage) {
2215	/*
2216	* The pages were successfully merged: insert new
2217	* node in the stable tree and add both rmap_items.
2218	*/
2219	lock_page(page: kpage);
2220	stable_node = stable_tree_insert(kpage);
2221	if (stable_node) {
2222	stable_tree_append(rmap_item: tree_rmap_item, stable_node,
2223	max_page_sharing_bypass: false);
2224	stable_tree_append(rmap_item, stable_node,
2225	max_page_sharing_bypass: false);
2226	}
2227	unlock_page(page: kpage);
2228
2229	/*
2230	* If we fail to insert the page into the stable tree,
2231	* we will have 2 virtual addresses that are pointing
2232	* to a ksm page left outside the stable tree,
2233	* in which case we need to break_cow on both.
2234	*/
2235	if (!stable_node) {
2236	break_cow(rmap_item: tree_rmap_item);
2237	break_cow(rmap_item);
2238	}
2239	} else if (split) {
2240	/*
2241	* We are here if we tried to merge two pages and
2242	* failed because they both belonged to the same
2243	* compound page. We will split the page now, but no
2244	* merging will take place.
2245	* We do not want to add the cost of a full lock; if
2246	* the page is locked, it is better to skip it and
2247	* perhaps try again later.
2248	*/
2249	if (!trylock_page(page))
2250	return;
2251	split_huge_page(page);
2252	unlock_page(page);
2253	}
2254	}
2255	}
2256
2257	static struct ksm_rmap_item *get_next_rmap_item(struct ksm_mm_slot *mm_slot,
2258	struct ksm_rmap_item **rmap_list,
2259	unsigned long addr)
2260	{
2261	struct ksm_rmap_item *rmap_item;
2262
2263	while (*rmap_list) {
2264	rmap_item = *rmap_list;
2265	if ((rmap_item->address & PAGE_MASK) == addr)
2266	return rmap_item;
2267	if (rmap_item->address > addr)
2268	break;
2269	*rmap_list = rmap_item->rmap_list;
2270	remove_rmap_item_from_tree(rmap_item);
2271	free_rmap_item(rmap_item);
2272	}
2273
2274	rmap_item = alloc_rmap_item();
2275	if (rmap_item) {
2276	/* It has already been zeroed */
2277	rmap_item->mm = mm_slot->slot.mm;
2278	rmap_item->mm->ksm_rmap_items++;
2279	rmap_item->address = addr;
2280	rmap_item->rmap_list = *rmap_list;
2281	*rmap_list = rmap_item;
2282	}
2283	return rmap_item;
2284	}
2285
2286	static struct ksm_rmap_item *scan_get_next_rmap_item(struct page **page)
2287	{
2288	struct mm_struct *mm;
2289	struct ksm_mm_slot *mm_slot;
2290	struct mm_slot *slot;
2291	struct vm_area_struct *vma;
2292	struct ksm_rmap_item *rmap_item;
2293	struct vma_iterator vmi;
2294	int nid;
2295
2296	if (list_empty(head: &ksm_mm_head.slot.mm_node))
2297	return NULL;
2298
2299	mm_slot = ksm_scan.mm_slot;
2300	if (mm_slot == &ksm_mm_head) {
2301	trace_ksm_start_scan(seq: ksm_scan.seqnr, rmap_entries: ksm_rmap_items);
2302
2303	/*
2304	* A number of pages can hang around indefinitely on per-cpu
2305	* pagevecs, raised page count preventing write_protect_page
2306	* from merging them. Though it doesn't really matter much,
2307	* it is puzzling to see some stuck in pages_volatile until
2308	* other activity jostles them out, and they also prevented
2309	* LTP's KSM test from succeeding deterministically; so drain
2310	* them here (here rather than on entry to ksm_do_scan(),
2311	* so we don't IPI too often when pages_to_scan is set low).
2312	*/
2313	lru_add_drain_all();
2314
2315	/*
2316	* Whereas stale stable_nodes on the stable_tree itself
2317	* get pruned in the regular course of stable_tree_search(),
2318	* those moved out to the migrate_nodes list can accumulate:
2319	* so prune them once before each full scan.
2320	*/
2321	if (!ksm_merge_across_nodes) {
2322	struct ksm_stable_node *stable_node, *next;
2323	struct page *page;
2324
2325	list_for_each_entry_safe(stable_node, next,
2326	&migrate_nodes, list) {
2327	page = get_ksm_page(stable_node,
2328	flags: GET_KSM_PAGE_NOLOCK);
2329	if (page)
2330	put_page(page);
2331	cond_resched();
2332	}
2333	}
2334
2335	for (nid = 0; nid < ksm_nr_node_ids; nid++)
2336	root_unstable_tree[nid] = RB_ROOT;
2337
2338	spin_lock(lock: &ksm_mmlist_lock);
2339	slot = list_entry(mm_slot->slot.mm_node.next,
2340	struct mm_slot, mm_node);
2341	mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot);
2342	ksm_scan.mm_slot = mm_slot;
2343	spin_unlock(lock: &ksm_mmlist_lock);
2344	/*
2345	* Although we tested list_empty() above, a racing __ksm_exit
2346	* of the last mm on the list may have removed it since then.
2347	*/
2348	if (mm_slot == &ksm_mm_head)
2349	return NULL;
2350	next_mm:
2351	ksm_scan.address = 0;
2352	ksm_scan.rmap_list = &mm_slot->rmap_list;
2353	}
2354
2355	slot = &mm_slot->slot;
2356	mm = slot->mm;
2357	vma_iter_init(vmi: &vmi, mm, addr: ksm_scan.address);
2358
2359	mmap_read_lock(mm);
2360	if (ksm_test_exit(mm))
2361	goto no_vmas;
2362
2363	for_each_vma(vmi, vma) {
2364	if (!(vma->vm_flags & VM_MERGEABLE))
2365	continue;
2366	if (ksm_scan.address < vma->vm_start)
2367	ksm_scan.address = vma->vm_start;
2368	if (!vma->anon_vma)
2369	ksm_scan.address = vma->vm_end;
2370
2371	while (ksm_scan.address < vma->vm_end) {
2372	if (ksm_test_exit(mm))
2373	break;
2374	*page = follow_page(vma, address: ksm_scan.address, foll_flags: FOLL_GET);
2375	if (IS_ERR_OR_NULL(ptr: *page)) {
2376	ksm_scan.address += PAGE_SIZE;
2377	cond_resched();
2378	continue;
2379	}
2380	if (is_zone_device_page(page: *page))
2381	goto next_page;
2382	if (PageAnon(page: *page)) {
2383	flush_anon_page(vma, page: *page, vmaddr: ksm_scan.address);
2384	flush_dcache_page(page: *page);
2385	rmap_item = get_next_rmap_item(mm_slot,
2386	rmap_list: ksm_scan.rmap_list, addr: ksm_scan.address);
2387	if (rmap_item) {
2388	ksm_scan.rmap_list =
2389	&rmap_item->rmap_list;
2390	ksm_scan.address += PAGE_SIZE;
2391	} else
2392	put_page(page: *page);
2393	mmap_read_unlock(mm);
2394	return rmap_item;
2395	}
2396	next_page:
2397	put_page(page: *page);
2398	ksm_scan.address += PAGE_SIZE;
2399	cond_resched();
2400	}
2401	}
2402
2403	if (ksm_test_exit(mm)) {
2404	no_vmas:
2405	ksm_scan.address = 0;
2406	ksm_scan.rmap_list = &mm_slot->rmap_list;
2407	}
2408	/*
2409	* Nuke all the rmap_items that are above this current rmap:
2410	* because there were no VM_MERGEABLE vmas with such addresses.
2411	*/
2412	remove_trailing_rmap_items(rmap_list: ksm_scan.rmap_list);
2413
2414	spin_lock(lock: &ksm_mmlist_lock);
2415	slot = list_entry(mm_slot->slot.mm_node.next,
2416	struct mm_slot, mm_node);
2417	ksm_scan.mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot);
2418	if (ksm_scan.address == 0) {
2419	/*
2420	* We've completed a full scan of all vmas, holding mmap_lock
2421	* throughout, and found no VM_MERGEABLE: so do the same as
2422	* __ksm_exit does to remove this mm from all our lists now.
2423	* This applies either when cleaning up after __ksm_exit
2424	* (but beware: we can reach here even before __ksm_exit),
2425	* or when all VM_MERGEABLE areas have been unmapped (and
2426	* mmap_lock then protects against race with MADV_MERGEABLE).
2427	*/
2428	hash_del(node: &mm_slot->slot.hash);
2429	list_del(entry: &mm_slot->slot.mm_node);
2430	spin_unlock(lock: &ksm_mmlist_lock);
2431
2432	mm_slot_free(cache: mm_slot_cache, objp: mm_slot);
2433	clear_bit(MMF_VM_MERGEABLE, addr: &mm->flags);
2434	clear_bit(MMF_VM_MERGE_ANY, addr: &mm->flags);
2435	mmap_read_unlock(mm);
2436	mmdrop(mm);
2437	} else {
2438	mmap_read_unlock(mm);
2439	/*
2440	* mmap_read_unlock(mm) first because after
2441	* spin_unlock(&ksm_mmlist_lock) run, the "mm" may
2442	* already have been freed under us by __ksm_exit()
2443	* because the "mm_slot" is still hashed and
2444	* ksm_scan.mm_slot doesn't point to it anymore.
2445	*/
2446	spin_unlock(lock: &ksm_mmlist_lock);
2447	}
2448
2449	/* Repeat until we've completed scanning the whole list */
2450	mm_slot = ksm_scan.mm_slot;
2451	if (mm_slot != &ksm_mm_head)
2452	goto next_mm;
2453
2454	trace_ksm_stop_scan(seq: ksm_scan.seqnr, rmap_entries: ksm_rmap_items);
2455	ksm_scan.seqnr++;
2456	return NULL;
2457	}
2458
2459	/**
2460	* ksm_do_scan - the ksm scanner main worker function.
2461	* @scan_npages: number of pages we want to scan before we return.
2462	*/
2463	static void ksm_do_scan(unsigned int scan_npages)
2464	{
2465	struct ksm_rmap_item *rmap_item;
2466	struct page *page;
2467
2468	while (scan_npages-- && likely(!freezing(current))) {
2469	cond_resched();
2470	rmap_item = scan_get_next_rmap_item(page: &page);
2471	if (!rmap_item)
2472	return;
2473	cmp_and_merge_page(page, rmap_item);
2474	put_page(page);
2475	}
2476	}
2477
2478	static int ksmd_should_run(void)
2479	{
2480	return (ksm_run & KSM_RUN_MERGE) && !list_empty(head: &ksm_mm_head.slot.mm_node);
2481	}
2482
2483	static int ksm_scan_thread(void *nothing)
2484	{
2485	unsigned int sleep_ms;
2486
2487	set_freezable();
2488	set_user_nice(current, nice: 5);
2489
2490	while (!kthread_should_stop()) {
2491	mutex_lock(lock: &ksm_thread_mutex);
2492	wait_while_offlining();
2493	if (ksmd_should_run())
2494	ksm_do_scan(scan_npages: ksm_thread_pages_to_scan);
2495	mutex_unlock(lock: &ksm_thread_mutex);
2496
2497	try_to_freeze();
2498
2499	if (ksmd_should_run()) {
2500	sleep_ms = READ_ONCE(ksm_thread_sleep_millisecs);
2501	wait_event_interruptible_timeout(ksm_iter_wait,
2502	sleep_ms != READ_ONCE(ksm_thread_sleep_millisecs),
2503	msecs_to_jiffies(sleep_ms));
2504	} else {
2505	wait_event_freezable(ksm_thread_wait,
2506	ksmd_should_run() || kthread_should_stop());
2507	}
2508	}
2509	return 0;
2510	}
2511
2512	static void __ksm_add_vma(struct vm_area_struct *vma)
2513	{
2514	unsigned long vm_flags = vma->vm_flags;
2515
2516	if (vm_flags & VM_MERGEABLE)
2517	return;
2518
2519	if (vma_ksm_compatible(vma))
2520	vm_flags_set(vma, VM_MERGEABLE);
2521	}
2522
2523	/**
2524	* ksm_add_vma - Mark vma as mergeable if compatible
2525	*
2526	* @vma: Pointer to vma
2527	*/
2528	void ksm_add_vma(struct vm_area_struct *vma)
2529	{
2530	struct mm_struct *mm = vma->vm_mm;
2531
2532	if (test_bit(MMF_VM_MERGE_ANY, &mm->flags))
2533	__ksm_add_vma(vma);
2534	}
2535
2536	static void ksm_add_vmas(struct mm_struct *mm)
2537	{
2538	struct vm_area_struct *vma;
2539
2540	VMA_ITERATOR(vmi, mm, 0);
2541	for_each_vma(vmi, vma)
2542	__ksm_add_vma(vma);
2543	}
2544
2545	/**
2546	* ksm_enable_merge_any - Add mm to mm ksm list and enable merging on all
2547	* compatible VMA's
2548	*
2549	* @mm: Pointer to mm
2550	*
2551	* Returns 0 on success, otherwise error code
2552	*/
2553	int ksm_enable_merge_any(struct mm_struct *mm)
2554	{
2555	int err;
2556
2557	if (test_bit(MMF_VM_MERGE_ANY, &mm->flags))
2558	return 0;
2559
2560	if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
2561	err = __ksm_enter(mm);
2562	if (err)
2563	return err;
2564	}
2565
2566	set_bit(MMF_VM_MERGE_ANY, addr: &mm->flags);
2567	ksm_add_vmas(mm);
2568
2569	return 0;
2570	}
2571
2572	int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
2573	unsigned long end, int advice, unsigned long *vm_flags)
2574	{
2575	struct mm_struct *mm = vma->vm_mm;
2576	int err;
2577
2578	switch (advice) {
2579	case MADV_MERGEABLE:
2580	if (vma->vm_flags & VM_MERGEABLE)
2581	return 0;
2582	if (!vma_ksm_compatible(vma))
2583	return 0;
2584
2585	if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
2586	err = __ksm_enter(mm);
2587	if (err)
2588	return err;
2589	}
2590
2591	*vm_flags |= VM_MERGEABLE;
2592	break;
2593
2594	case MADV_UNMERGEABLE:
2595	if (!(*vm_flags & VM_MERGEABLE))
2596	return 0; /* just ignore the advice */
2597
2598	if (vma->anon_vma) {
2599	err = unmerge_ksm_pages(vma, start, end);
2600	if (err)
2601	return err;
2602	}
2603
2604	*vm_flags &= ~VM_MERGEABLE;
2605	break;
2606	}
2607
2608	return 0;
2609	}
2610	EXPORT_SYMBOL_GPL(ksm_madvise);
2611
2612	int __ksm_enter(struct mm_struct *mm)
2613	{
2614	struct ksm_mm_slot *mm_slot;
2615	struct mm_slot *slot;
2616	int needs_wakeup;
2617
2618	mm_slot = mm_slot_alloc(cache: mm_slot_cache);
2619	if (!mm_slot)
2620	return -ENOMEM;
2621
2622	slot = &mm_slot->slot;
2623
2624	/* Check ksm_run too? Would need tighter locking */
2625	needs_wakeup = list_empty(head: &ksm_mm_head.slot.mm_node);
2626
2627	spin_lock(lock: &ksm_mmlist_lock);
2628	mm_slot_insert(mm_slots_hash, mm, slot);
2629	/*
2630	* When KSM_RUN_MERGE (or KSM_RUN_STOP),
2631	* insert just behind the scanning cursor, to let the area settle
2632	* down a little; when fork is followed by immediate exec, we don't
2633	* want ksmd to waste time setting up and tearing down an rmap_list.
2634	*
2635	* But when KSM_RUN_UNMERGE, it's important to insert ahead of its
2636	* scanning cursor, otherwise KSM pages in newly forked mms will be
2637	* missed: then we might as well insert at the end of the list.
2638	*/
2639	if (ksm_run & KSM_RUN_UNMERGE)
2640	list_add_tail(new: &slot->mm_node, head: &ksm_mm_head.slot.mm_node);
2641	else
2642	list_add_tail(new: &slot->mm_node, head: &ksm_scan.mm_slot->slot.mm_node);
2643	spin_unlock(lock: &ksm_mmlist_lock);
2644
2645	set_bit(MMF_VM_MERGEABLE, addr: &mm->flags);
2646	mmgrab(mm);
2647
2648	if (needs_wakeup)
2649	wake_up_interruptible(&ksm_thread_wait);
2650
2651	trace_ksm_enter(mm);
2652	return 0;
2653	}
2654
2655	void __ksm_exit(struct mm_struct *mm)
2656	{
2657	struct ksm_mm_slot *mm_slot;
2658	struct mm_slot *slot;
2659	int easy_to_free = 0;
2660
2661	/*
2662	* This process is exiting: if it's straightforward (as is the
2663	* case when ksmd was never running), free mm_slot immediately.
2664	* But if it's at the cursor or has rmap_items linked to it, use
2665	* mmap_lock to synchronize with any break_cows before pagetables
2666	* are freed, and leave the mm_slot on the list for ksmd to free.
2667	* Beware: ksm may already have noticed it exiting and freed the slot.
2668	*/
2669
2670	spin_lock(lock: &ksm_mmlist_lock);
2671	slot = mm_slot_lookup(mm_slots_hash, mm);
2672	mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot);
2673	if (mm_slot && ksm_scan.mm_slot != mm_slot) {
2674	if (!mm_slot->rmap_list) {
2675	hash_del(node: &slot->hash);
2676	list_del(entry: &slot->mm_node);
2677	easy_to_free = 1;
2678	} else {
2679	list_move(list: &slot->mm_node,
2680	head: &ksm_scan.mm_slot->slot.mm_node);
2681	}
2682	}
2683	spin_unlock(lock: &ksm_mmlist_lock);
2684
2685	if (easy_to_free) {
2686	mm_slot_free(cache: mm_slot_cache, objp: mm_slot);
2687	clear_bit(MMF_VM_MERGE_ANY, addr: &mm->flags);
2688	clear_bit(MMF_VM_MERGEABLE, addr: &mm->flags);
2689	mmdrop(mm);
2690	} else if (mm_slot) {
2691	mmap_write_lock(mm);
2692	mmap_write_unlock(mm);
2693	}
2694
2695	trace_ksm_exit(mm);
2696	}
2697
2698	struct page *ksm_might_need_to_copy(struct page *page,
2699	struct vm_area_struct *vma, unsigned long address)
2700	{
2701	struct folio *folio = page_folio(page);
2702	struct anon_vma *anon_vma = folio_anon_vma(folio);
2703	struct page *new_page;
2704
2705	if (PageKsm(page)) {
2706	if (page_stable_node(page) &&
2707	!(ksm_run & KSM_RUN_UNMERGE))
2708	return page; /* no need to copy it */
2709	} else if (!anon_vma) {
2710	return page; /* no need to copy it */
2711	} else if (page->index == linear_page_index(vma, address) &&
2712	anon_vma->root == vma->anon_vma->root) {
2713	return page; /* still no need to copy it */
2714	}
2715	if (!PageUptodate(page))
2716	return page; /* let do_swap_page report the error */
2717
2718	new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, addr: address);
2719	if (new_page &&
2720	mem_cgroup_charge(page_folio(new_page), mm: vma->vm_mm, GFP_KERNEL)) {
2721	put_page(page: new_page);
2722	new_page = NULL;
2723	}
2724	if (new_page) {
2725	if (copy_mc_user_highpage(to: new_page, from: page, vaddr: address, vma)) {
2726	put_page(page: new_page);
2727	memory_failure_queue(page_to_pfn(page), flags: 0);
2728	return ERR_PTR(-EHWPOISON);
2729	}
2730	SetPageDirty(new_page);
2731	__SetPageUptodate(page: new_page);
2732	__SetPageLocked(page: new_page);
2733	#ifdef CONFIG_SWAP
2734	count_vm_event(KSM_SWPIN_COPY);
2735	#endif
2736	}
2737
2738	return new_page;
2739	}
2740
2741	void rmap_walk_ksm(struct folio *folio, struct rmap_walk_control *rwc)
2742	{
2743	struct ksm_stable_node *stable_node;
2744	struct ksm_rmap_item *rmap_item;
2745	int search_new_forks = 0;
2746
2747	VM_BUG_ON_FOLIO(!folio_test_ksm(folio), folio);
2748
2749	/*
2750	* Rely on the page lock to protect against concurrent modifications
2751	* to that page's node of the stable tree.
2752	*/
2753	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
2754
2755	stable_node = folio_stable_node(folio);
2756	if (!stable_node)
2757	return;
2758	again:
2759	hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
2760	struct anon_vma *anon_vma = rmap_item->anon_vma;
2761	struct anon_vma_chain *vmac;
2762	struct vm_area_struct *vma;
2763
2764	cond_resched();
2765	if (!anon_vma_trylock_read(anon_vma)) {
2766	if (rwc->try_lock) {
2767	rwc->contended = true;
2768	return;
2769	}
2770	anon_vma_lock_read(anon_vma);
2771	}
2772	anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
2773	0, ULONG_MAX) {
2774	unsigned long addr;
2775
2776	cond_resched();
2777	vma = vmac->vma;
2778
2779	/* Ignore the stable/unstable/sqnr flags */
2780	addr = rmap_item->address & PAGE_MASK;
2781
2782	if (addr < vma->vm_start || addr >= vma->vm_end)
2783	continue;
2784	/*
2785	* Initially we examine only the vma which covers this
2786	* rmap_item; but later, if there is still work to do,
2787	* we examine covering vmas in other mms: in case they
2788	* were forked from the original since ksmd passed.
2789	*/
2790	if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
2791	continue;
2792
2793	if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg))
2794	continue;
2795
2796	if (!rwc->rmap_one(folio, vma, addr, rwc->arg)) {
2797	anon_vma_unlock_read(anon_vma);
2798	return;
2799	}
2800	if (rwc->done && rwc->done(folio)) {
2801	anon_vma_unlock_read(anon_vma);
2802	return;
2803	}
2804	}
2805	anon_vma_unlock_read(anon_vma);
2806	}
2807	if (!search_new_forks++)
2808	goto again;
2809	}
2810
2811	#ifdef CONFIG_MEMORY_FAILURE
2812	/*
2813	* Collect processes when the error hit an ksm page.
2814	*/
2815	void collect_procs_ksm(struct page *page, struct list_head *to_kill,
2816	int force_early)
2817	{
2818	struct ksm_stable_node *stable_node;
2819	struct ksm_rmap_item *rmap_item;
2820	struct folio *folio = page_folio(page);
2821	struct vm_area_struct *vma;
2822	struct task_struct *tsk;
2823
2824	stable_node = folio_stable_node(folio);
2825	if (!stable_node)
2826	return;
2827	hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
2828	struct anon_vma *av = rmap_item->anon_vma;
2829
2830	anon_vma_lock_read(av);
2831	read_lock(&tasklist_lock);
2832	for_each_process(tsk) {
2833	struct anon_vma_chain *vmac;
2834	unsigned long addr;
2835	struct task_struct *t =
2836	task_early_kill(tsk, force_early);
2837	if (!t)
2838	continue;
2839	anon_vma_interval_tree_foreach(vmac, &av->rb_root, 0,
2840	ULONG_MAX)
2841	{
2842	vma = vmac->vma;
2843	if (vma->vm_mm == t->mm) {
2844	addr = rmap_item->address & PAGE_MASK;
2845	add_to_kill_ksm(t, page, vma, to_kill,
2846	addr);
2847	}
2848	}
2849	}
2850	read_unlock(&tasklist_lock);
2851	anon_vma_unlock_read(av);
2852	}
2853	}
2854	#endif
2855
2856	#ifdef CONFIG_MIGRATION
2857	void folio_migrate_ksm(struct folio *newfolio, struct folio *folio)
2858	{
2859	struct ksm_stable_node *stable_node;
2860
2861	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
2862	VM_BUG_ON_FOLIO(!folio_test_locked(newfolio), newfolio);
2863	VM_BUG_ON_FOLIO(newfolio->mapping != folio->mapping, newfolio);
2864
2865	stable_node = folio_stable_node(folio);
2866	if (stable_node) {
2867	VM_BUG_ON_FOLIO(stable_node->kpfn != folio_pfn(folio), folio);
2868	stable_node->kpfn = folio_pfn(newfolio);
2869	/*
2870	* newfolio->mapping was set in advance; now we need smp_wmb()
2871	* to make sure that the new stable_node->kpfn is visible
2872	* to get_ksm_page() before it can see that folio->mapping
2873	* has gone stale (or that folio_test_swapcache has been cleared).
2874	*/
2875	smp_wmb();
2876	set_page_stable_node(&folio->page, NULL);
2877	}
2878	}
2879	#endif /* CONFIG_MIGRATION */
2880
2881	#ifdef CONFIG_MEMORY_HOTREMOVE
2882	static void wait_while_offlining(void)
2883	{
2884	while (ksm_run & KSM_RUN_OFFLINE) {
2885	mutex_unlock(&ksm_thread_mutex);
2886	wait_on_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE),
2887	TASK_UNINTERRUPTIBLE);
2888	mutex_lock(&ksm_thread_mutex);
2889	}
2890	}
2891
2892	static bool stable_node_dup_remove_range(struct ksm_stable_node *stable_node,
2893	unsigned long start_pfn,
2894	unsigned long end_pfn)
2895	{
2896	if (stable_node->kpfn >= start_pfn &&
2897	stable_node->kpfn < end_pfn) {
2898	/*
2899	* Don't get_ksm_page, page has already gone:
2900	* which is why we keep kpfn instead of page*
2901	*/
2902	remove_node_from_stable_tree(stable_node);
2903	return true;
2904	}
2905	return false;
2906	}
2907
2908	static bool stable_node_chain_remove_range(struct ksm_stable_node *stable_node,
2909	unsigned long start_pfn,
2910	unsigned long end_pfn,
2911	struct rb_root *root)
2912	{
2913	struct ksm_stable_node *dup;
2914	struct hlist_node *hlist_safe;
2915
2916	if (!is_stable_node_chain(stable_node)) {
2917	VM_BUG_ON(is_stable_node_dup(stable_node));
2918	return stable_node_dup_remove_range(stable_node, start_pfn,
2919	end_pfn);
2920	}
2921
2922	hlist_for_each_entry_safe(dup, hlist_safe,
2923	&stable_node->hlist, hlist_dup) {
2924	VM_BUG_ON(!is_stable_node_dup(dup));
2925	stable_node_dup_remove_range(dup, start_pfn, end_pfn);
2926	}
2927	if (hlist_empty(&stable_node->hlist)) {
2928	free_stable_node_chain(stable_node, root);
2929	return true; /* notify caller that tree was rebalanced */
2930	} else
2931	return false;
2932	}
2933
2934	static void ksm_check_stable_tree(unsigned long start_pfn,
2935	unsigned long end_pfn)
2936	{
2937	struct ksm_stable_node *stable_node, *next;
2938	struct rb_node *node;
2939	int nid;
2940
2941	for (nid = 0; nid < ksm_nr_node_ids; nid++) {
2942	node = rb_first(root_stable_tree + nid);
2943	while (node) {
2944	stable_node = rb_entry(node, struct ksm_stable_node, node);
2945	if (stable_node_chain_remove_range(stable_node,
2946	start_pfn, end_pfn,
2947	root_stable_tree +
2948	nid))
2949	node = rb_first(root_stable_tree + nid);
2950	else
2951	node = rb_next(node);
2952	cond_resched();
2953	}
2954	}
2955	list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) {
2956	if (stable_node->kpfn >= start_pfn &&
2957	stable_node->kpfn < end_pfn)
2958	remove_node_from_stable_tree(stable_node);
2959	cond_resched();
2960	}
2961	}
2962
2963	static int ksm_memory_callback(struct notifier_block *self,
2964	unsigned long action, void *arg)
2965	{
2966	struct memory_notify *mn = arg;
2967
2968	switch (action) {
2969	case MEM_GOING_OFFLINE:
2970	/*
2971	* Prevent ksm_do_scan(), unmerge_and_remove_all_rmap_items()
2972	* and remove_all_stable_nodes() while memory is going offline:
2973	* it is unsafe for them to touch the stable tree at this time.
2974	* But unmerge_ksm_pages(), rmap lookups and other entry points
2975	* which do not need the ksm_thread_mutex are all safe.
2976	*/
2977	mutex_lock(&ksm_thread_mutex);
2978	ksm_run |= KSM_RUN_OFFLINE;
2979	mutex_unlock(&ksm_thread_mutex);
2980	break;
2981
2982	case MEM_OFFLINE:
2983	/*
2984	* Most of the work is done by page migration; but there might
2985	* be a few stable_nodes left over, still pointing to struct
2986	* pages which have been offlined: prune those from the tree,
2987	* otherwise get_ksm_page() might later try to access a
2988	* non-existent struct page.
2989	*/
2990	ksm_check_stable_tree(mn->start_pfn,
2991	mn->start_pfn + mn->nr_pages);
2992	fallthrough;
2993	case MEM_CANCEL_OFFLINE:
2994	mutex_lock(&ksm_thread_mutex);
2995	ksm_run &= ~KSM_RUN_OFFLINE;
2996	mutex_unlock(&ksm_thread_mutex);
2997
2998	smp_mb(); /* wake_up_bit advises this */
2999	wake_up_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE));
3000	break;
3001	}
3002	return NOTIFY_OK;
3003	}
3004	#else
3005	static void wait_while_offlining(void)
3006	{
3007	}
3008	#endif /* CONFIG_MEMORY_HOTREMOVE */
3009
3010	#ifdef CONFIG_PROC_FS
3011	long ksm_process_profit(struct mm_struct *mm)
3012	{
3013	return mm->ksm_merging_pages * PAGE_SIZE -
3014	mm->ksm_rmap_items * sizeof(struct ksm_rmap_item);
3015	}
3016	#endif /* CONFIG_PROC_FS */
3017
3018	#ifdef CONFIG_SYSFS
3019	/*
3020	* This all compiles without CONFIG_SYSFS, but is a waste of space.
3021	*/
3022
3023	#define KSM_ATTR_RO(_name) \
3024	static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
3025	#define KSM_ATTR(_name) \
3026	static struct kobj_attribute _name##_attr = __ATTR_RW(_name)
3027
3028	static ssize_t sleep_millisecs_show(struct kobject *kobj,
3029	struct kobj_attribute *attr, char *buf)
3030	{
3031	return sysfs_emit(buf, "%u\n", ksm_thread_sleep_millisecs);
3032	}
3033
3034	static ssize_t sleep_millisecs_store(struct kobject *kobj,
3035	struct kobj_attribute *attr,
3036	const char *buf, size_t count)
3037	{
3038	unsigned int msecs;
3039	int err;
3040
3041	err = kstrtouint(buf, 10, &msecs);
3042	if (err)
3043	return -EINVAL;
3044
3045	ksm_thread_sleep_millisecs = msecs;
3046	wake_up_interruptible(&ksm_iter_wait);
3047
3048	return count;
3049	}
3050	KSM_ATTR(sleep_millisecs);
3051
3052	static ssize_t pages_to_scan_show(struct kobject *kobj,
3053	struct kobj_attribute *attr, char *buf)
3054	{
3055	return sysfs_emit(buf, "%u\n", ksm_thread_pages_to_scan);
3056	}
3057
3058	static ssize_t pages_to_scan_store(struct kobject *kobj,
3059	struct kobj_attribute *attr,
3060	const char *buf, size_t count)
3061	{
3062	unsigned int nr_pages;
3063	int err;
3064
3065	err = kstrtouint(buf, 10, &nr_pages);
3066	if (err)
3067	return -EINVAL;
3068
3069	ksm_thread_pages_to_scan = nr_pages;
3070
3071	return count;
3072	}
3073	KSM_ATTR(pages_to_scan);
3074
3075	static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
3076	char *buf)
3077	{
3078	return sysfs_emit(buf, "%lu\n", ksm_run);
3079	}
3080
3081	static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
3082	const char *buf, size_t count)
3083	{
3084	unsigned int flags;
3085	int err;
3086
3087	err = kstrtouint(buf, 10, &flags);
3088	if (err)
3089	return -EINVAL;
3090	if (flags > KSM_RUN_UNMERGE)
3091	return -EINVAL;
3092
3093	/*
3094	* KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
3095	* KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
3096	* breaking COW to free the pages_shared (but leaves mm_slots
3097	* on the list for when ksmd may be set running again).
3098	*/
3099
3100	mutex_lock(&ksm_thread_mutex);
3101	wait_while_offlining();
3102	if (ksm_run != flags) {
3103	ksm_run = flags;
3104	if (flags & KSM_RUN_UNMERGE) {
3105	set_current_oom_origin();
3106	err = unmerge_and_remove_all_rmap_items();
3107	clear_current_oom_origin();
3108	if (err) {
3109	ksm_run = KSM_RUN_STOP;
3110	count = err;
3111	}
3112	}
3113	}
3114	mutex_unlock(&ksm_thread_mutex);
3115
3116	if (flags & KSM_RUN_MERGE)
3117	wake_up_interruptible(&ksm_thread_wait);
3118
3119	return count;
3120	}
3121	KSM_ATTR(run);
3122
3123	#ifdef CONFIG_NUMA
3124	static ssize_t merge_across_nodes_show(struct kobject *kobj,
3125	struct kobj_attribute *attr, char *buf)
3126	{
3127	return sysfs_emit(buf, "%u\n", ksm_merge_across_nodes);
3128	}
3129
3130	static ssize_t merge_across_nodes_store(struct kobject *kobj,
3131	struct kobj_attribute *attr,
3132	const char *buf, size_t count)
3133	{
3134	int err;
3135	unsigned long knob;
3136
3137	err = kstrtoul(buf, 10, &knob);
3138	if (err)
3139	return err;
3140	if (knob > 1)
3141	return -EINVAL;
3142
3143	mutex_lock(&ksm_thread_mutex);
3144	wait_while_offlining();
3145	if (ksm_merge_across_nodes != knob) {
3146	if (ksm_pages_shared || remove_all_stable_nodes())
3147	err = -EBUSY;
3148	else if (root_stable_tree == one_stable_tree) {
3149	struct rb_root *buf;
3150	/*
3151	* This is the first time that we switch away from the
3152	* default of merging across nodes: must now allocate
3153	* a buffer to hold as many roots as may be needed.
3154	* Allocate stable and unstable together:
3155	* MAXSMP NODES_SHIFT 10 will use 16kB.
3156	*/
3157	buf = kcalloc(nr_node_ids + nr_node_ids, sizeof(*buf),
3158	GFP_KERNEL);
3159	/* Let us assume that RB_ROOT is NULL is zero */
3160	if (!buf)
3161	err = -ENOMEM;
3162	else {
3163	root_stable_tree = buf;
3164	root_unstable_tree = buf + nr_node_ids;
3165	/* Stable tree is empty but not the unstable */
3166	root_unstable_tree[0] = one_unstable_tree[0];
3167	}
3168	}
3169	if (!err) {
3170	ksm_merge_across_nodes = knob;
3171	ksm_nr_node_ids = knob ? 1 : nr_node_ids;
3172	}
3173	}
3174	mutex_unlock(&ksm_thread_mutex);
3175
3176	return err ? err : count;
3177	}
3178	KSM_ATTR(merge_across_nodes);
3179	#endif
3180
3181	static ssize_t use_zero_pages_show(struct kobject *kobj,
3182	struct kobj_attribute *attr, char *buf)
3183	{
3184	return sysfs_emit(buf, "%u\n", ksm_use_zero_pages);
3185	}
3186	static ssize_t use_zero_pages_store(struct kobject *kobj,
3187	struct kobj_attribute *attr,
3188	const char *buf, size_t count)
3189	{
3190	int err;
3191	bool value;
3192
3193	err = kstrtobool(buf, &value);
3194	if (err)
3195	return -EINVAL;
3196
3197	ksm_use_zero_pages = value;
3198
3199	return count;
3200	}
3201	KSM_ATTR(use_zero_pages);
3202
3203	static ssize_t max_page_sharing_show(struct kobject *kobj,
3204	struct kobj_attribute *attr, char *buf)
3205	{
3206	return sysfs_emit(buf, "%u\n", ksm_max_page_sharing);
3207	}
3208
3209	static ssize_t max_page_sharing_store(struct kobject *kobj,
3210	struct kobj_attribute *attr,
3211	const char *buf, size_t count)
3212	{
3213	int err;
3214	int knob;
3215
3216	err = kstrtoint(buf, 10, &knob);
3217	if (err)
3218	return err;
3219	/*
3220	* When a KSM page is created it is shared by 2 mappings. This
3221	* being a signed comparison, it implicitly verifies it's not
3222	* negative.
3223	*/
3224	if (knob < 2)
3225	return -EINVAL;
3226
3227	if (READ_ONCE(ksm_max_page_sharing) == knob)
3228	return count;
3229
3230	mutex_lock(&ksm_thread_mutex);
3231	wait_while_offlining();
3232	if (ksm_max_page_sharing != knob) {
3233	if (ksm_pages_shared || remove_all_stable_nodes())
3234	err = -EBUSY;
3235	else
3236	ksm_max_page_sharing = knob;
3237	}
3238	mutex_unlock(&ksm_thread_mutex);
3239
3240	return err ? err : count;
3241	}
3242	KSM_ATTR(max_page_sharing);
3243
3244	static ssize_t pages_shared_show(struct kobject *kobj,
3245	struct kobj_attribute *attr, char *buf)
3246	{
3247	return sysfs_emit(buf, "%lu\n", ksm_pages_shared);
3248	}
3249	KSM_ATTR_RO(pages_shared);
3250
3251	static ssize_t pages_sharing_show(struct kobject *kobj,
3252	struct kobj_attribute *attr, char *buf)
3253	{
3254	return sysfs_emit(buf, "%lu\n", ksm_pages_sharing);
3255	}
3256	KSM_ATTR_RO(pages_sharing);
3257
3258	static ssize_t pages_unshared_show(struct kobject *kobj,
3259	struct kobj_attribute *attr, char *buf)
3260	{
3261	return sysfs_emit(buf, "%lu\n", ksm_pages_unshared);
3262	}
3263	KSM_ATTR_RO(pages_unshared);
3264
3265	static ssize_t pages_volatile_show(struct kobject *kobj,
3266	struct kobj_attribute *attr, char *buf)
3267	{
3268	long ksm_pages_volatile;
3269
3270	ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
3271	- ksm_pages_sharing - ksm_pages_unshared;
3272	/*
3273	* It was not worth any locking to calculate that statistic,
3274	* but it might therefore sometimes be negative: conceal that.
3275	*/
3276	if (ksm_pages_volatile < 0)
3277	ksm_pages_volatile = 0;
3278	return sysfs_emit(buf, "%ld\n", ksm_pages_volatile);
3279	}
3280	KSM_ATTR_RO(pages_volatile);
3281
3282	static ssize_t general_profit_show(struct kobject *kobj,
3283	struct kobj_attribute *attr, char *buf)
3284	{
3285	long general_profit;
3286
3287	general_profit = ksm_pages_sharing * PAGE_SIZE -
3288	ksm_rmap_items * sizeof(struct ksm_rmap_item);
3289
3290	return sysfs_emit(buf, "%ld\n", general_profit);
3291	}
3292	KSM_ATTR_RO(general_profit);
3293
3294	static ssize_t stable_node_dups_show(struct kobject *kobj,
3295	struct kobj_attribute *attr, char *buf)
3296	{
3297	return sysfs_emit(buf, "%lu\n", ksm_stable_node_dups);
3298	}
3299	KSM_ATTR_RO(stable_node_dups);
3300
3301	static ssize_t stable_node_chains_show(struct kobject *kobj,
3302	struct kobj_attribute *attr, char *buf)
3303	{
3304	return sysfs_emit(buf, "%lu\n", ksm_stable_node_chains);
3305	}
3306	KSM_ATTR_RO(stable_node_chains);
3307
3308	static ssize_t
3309	stable_node_chains_prune_millisecs_show(struct kobject *kobj,
3310	struct kobj_attribute *attr,
3311	char *buf)
3312	{
3313	return sysfs_emit(buf, "%u\n", ksm_stable_node_chains_prune_millisecs);
3314	}
3315
3316	static ssize_t
3317	stable_node_chains_prune_millisecs_store(struct kobject *kobj,
3318	struct kobj_attribute *attr,
3319	const char *buf, size_t count)
3320	{
3321	unsigned int msecs;
3322	int err;
3323
3324	err = kstrtouint(buf, 10, &msecs);
3325	if (err)
3326	return -EINVAL;
3327
3328	ksm_stable_node_chains_prune_millisecs = msecs;
3329
3330	return count;
3331	}
3332	KSM_ATTR(stable_node_chains_prune_millisecs);
3333
3334	static ssize_t full_scans_show(struct kobject *kobj,
3335	struct kobj_attribute *attr, char *buf)
3336	{
3337	return sysfs_emit(buf, "%lu\n", ksm_scan.seqnr);
3338	}
3339	KSM_ATTR_RO(full_scans);
3340
3341	static struct attribute *ksm_attrs[] = {
3342	&sleep_millisecs_attr.attr,
3343	&pages_to_scan_attr.attr,
3344	&run_attr.attr,
3345	&pages_shared_attr.attr,
3346	&pages_sharing_attr.attr,
3347	&pages_unshared_attr.attr,
3348	&pages_volatile_attr.attr,
3349	&full_scans_attr.attr,
3350	#ifdef CONFIG_NUMA
3351	&merge_across_nodes_attr.attr,
3352	#endif
3353	&max_page_sharing_attr.attr,
3354	&stable_node_chains_attr.attr,
3355	&stable_node_dups_attr.attr,
3356	&stable_node_chains_prune_millisecs_attr.attr,
3357	&use_zero_pages_attr.attr,
3358	&general_profit_attr.attr,
3359	NULL,
3360	};
3361
3362	static const struct attribute_group ksm_attr_group = {
3363	.attrs = ksm_attrs,
3364	.name = "ksm",
3365	};
3366	#endif /* CONFIG_SYSFS */
3367
3368	static int __init ksm_init(void)
3369	{
3370	struct task_struct *ksm_thread;
3371	int err;
3372
3373	/* The correct value depends on page size and endianness */
3374	zero_checksum = calc_checksum(ZERO_PAGE(0));
3375	/* Default to false for backwards compatibility */
3376	ksm_use_zero_pages = false;
3377
3378	err = ksm_slab_init();
3379	if (err)
3380	goto out;
3381
3382	ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
3383	if (IS_ERR(ptr: ksm_thread)) {
3384	pr_err("ksm: creating kthread failed\n");
3385	err = PTR_ERR(ptr: ksm_thread);
3386	goto out_free;
3387	}
3388
3389	#ifdef CONFIG_SYSFS
3390	err = sysfs_create_group(mm_kobj, &ksm_attr_group);
3391	if (err) {
3392	pr_err("ksm: register sysfs failed\n");
3393	kthread_stop(ksm_thread);
3394	goto out_free;
3395	}
3396	#else
3397	ksm_run = KSM_RUN_MERGE; /* no way for user to start it */
3398
3399	#endif /* CONFIG_SYSFS */
3400
3401	#ifdef CONFIG_MEMORY_HOTREMOVE
3402	/* There is no significance to this priority 100 */
3403	hotplug_memory_notifier(ksm_memory_callback, KSM_CALLBACK_PRI);
3404	#endif
3405	return 0;
3406
3407	out_free:
3408	ksm_slab_free();
3409	out:
3410	return err;
3411	}
3412	subsys_initcall(ksm_init);
3413