1// SPDX-License-Identifier: GPL-2.0
2/*
3 * linux/mm/page_isolation.c
4 */
5
6#include <linux/mm.h>
7#include <linux/page-isolation.h>
8#include <linux/pageblock-flags.h>
9#include <linux/memory.h>
10#include <linux/hugetlb.h>
11#include <linux/page_owner.h>
12#include <linux/migrate.h>
13#include "internal.h"
14
15#define CREATE_TRACE_POINTS
16#include <trace/events/page_isolation.h>
17
18/*
19 * This function checks whether the range [start_pfn, end_pfn) includes
20 * unmovable pages or not. The range must fall into a single pageblock and
21 * consequently belong to a single zone.
22 *
23 * PageLRU check without isolation or lru_lock could race so that
24 * MIGRATE_MOVABLE block might include unmovable pages. Similarly, pages
25 * with movable_ops can only be identified some time after they were
26 * allocated. So you can't expect this function should be exact.
27 *
28 * Returns a page without holding a reference. If the caller wants to
29 * dereference that page (e.g., dumping), it has to make sure that it
30 * cannot get removed (e.g., via memory unplug) concurrently.
31 *
32 */
33static struct page *has_unmovable_pages(unsigned long start_pfn, unsigned long end_pfn,
34 enum pb_isolate_mode mode)
35{
36 struct page *page = pfn_to_page(start_pfn);
37 struct zone *zone = page_zone(page);
38 unsigned long pfn;
39
40 VM_BUG_ON(pageblock_start_pfn(start_pfn) !=
41 pageblock_start_pfn(end_pfn - 1));
42
43 if (is_migrate_cma_page(page)) {
44 /*
45 * CMA allocations (alloc_contig_range) really need to mark
46 * isolate CMA pageblocks even when they are not movable in fact
47 * so consider them movable here.
48 */
49 if (mode == PB_ISOLATE_MODE_CMA_ALLOC)
50 return NULL;
51
52 return page;
53 }
54
55 for (pfn = start_pfn; pfn < end_pfn; pfn++) {
56 page = pfn_to_page(pfn);
57
58 /*
59 * Both, bootmem allocations and memory holes are marked
60 * PG_reserved and are unmovable. We can even have unmovable
61 * allocations inside ZONE_MOVABLE, for example when
62 * specifying "movablecore".
63 */
64 if (PageReserved(page))
65 return page;
66
67 /*
68 * If the zone is movable and we have ruled out all reserved
69 * pages then it should be reasonably safe to assume the rest
70 * is movable.
71 */
72 if (zone_idx(zone) == ZONE_MOVABLE)
73 continue;
74
75 /*
76 * Hugepages are not in LRU lists, but they're movable.
77 * THPs are on the LRU, but need to be counted as #small pages.
78 * We need not scan over tail pages because we don't
79 * handle each tail page individually in migration.
80 */
81 if (PageHuge(page) || PageTransCompound(page)) {
82 struct folio *folio = page_folio(page);
83 unsigned int skip_pages;
84
85 if (PageHuge(page)) {
86 struct hstate *h;
87
88 /*
89 * The huge page may be freed so can not
90 * use folio_hstate() directly.
91 */
92 h = size_to_hstate(size: folio_size(folio));
93 if (h && !hugepage_migration_supported(h))
94 return page;
95 } else if (!folio_test_lru(folio)) {
96 return page;
97 }
98
99 skip_pages = folio_nr_pages(folio) - folio_page_idx(folio, page);
100 pfn += skip_pages - 1;
101 continue;
102 }
103
104 /*
105 * We can't use page_count without pin a page
106 * because another CPU can free compound page.
107 * This check already skips compound tails of THP
108 * because their page->_refcount is zero at all time.
109 */
110 if (!page_ref_count(page)) {
111 if (PageBuddy(page))
112 pfn += (1 << buddy_order(page)) - 1;
113 continue;
114 }
115
116 /*
117 * The HWPoisoned page may be not in buddy system, and
118 * page_count() is not 0.
119 */
120 if ((mode == PB_ISOLATE_MODE_MEM_OFFLINE) && PageHWPoison(page))
121 continue;
122
123 /*
124 * We treat all PageOffline() pages as movable when offlining
125 * to give drivers a chance to decrement their reference count
126 * in MEM_GOING_OFFLINE in order to indicate that these pages
127 * can be offlined as there are no direct references anymore.
128 * For actually unmovable PageOffline() where the driver does
129 * not support this, we will fail later when trying to actually
130 * move these pages that still have a reference count > 0.
131 * (false negatives in this function only)
132 */
133 if ((mode == PB_ISOLATE_MODE_MEM_OFFLINE) && PageOffline(page))
134 continue;
135
136 if (PageLRU(page) || page_has_movable_ops(page))
137 continue;
138
139 /*
140 * If there are RECLAIMABLE pages, we need to check
141 * it. But now, memory offline itself doesn't call
142 * shrink_node_slabs() and it still to be fixed.
143 */
144 return page;
145 }
146 return NULL;
147}
148
149/*
150 * This function set pageblock migratetype to isolate if no unmovable page is
151 * present in [start_pfn, end_pfn). The pageblock must intersect with
152 * [start_pfn, end_pfn).
153 */
154static int set_migratetype_isolate(struct page *page, enum pb_isolate_mode mode,
155 unsigned long start_pfn, unsigned long end_pfn)
156{
157 struct zone *zone = page_zone(page);
158 struct page *unmovable;
159 unsigned long flags;
160 unsigned long check_unmovable_start, check_unmovable_end;
161
162 if (PageUnaccepted(page))
163 accept_page(page);
164
165 spin_lock_irqsave(&zone->lock, flags);
166
167 /*
168 * We assume the caller intended to SET migrate type to isolate.
169 * If it is already set, then someone else must have raced and
170 * set it before us.
171 */
172 if (is_migrate_isolate_page(page)) {
173 spin_unlock_irqrestore(lock: &zone->lock, flags);
174 return -EBUSY;
175 }
176
177 /*
178 * FIXME: Now, memory hotplug doesn't call shrink_slab() by itself.
179 * We just check MOVABLE pages.
180 *
181 * Pass the intersection of [start_pfn, end_pfn) and the page's pageblock
182 * to avoid redundant checks.
183 */
184 check_unmovable_start = max(page_to_pfn(page), start_pfn);
185 check_unmovable_end = min(pageblock_end_pfn(page_to_pfn(page)),
186 end_pfn);
187
188 unmovable = has_unmovable_pages(start_pfn: check_unmovable_start, end_pfn: check_unmovable_end,
189 mode);
190 if (!unmovable) {
191 if (!pageblock_isolate_and_move_free_pages(zone, page)) {
192 spin_unlock_irqrestore(lock: &zone->lock, flags);
193 return -EBUSY;
194 }
195 zone->nr_isolate_pageblock++;
196 spin_unlock_irqrestore(lock: &zone->lock, flags);
197 return 0;
198 }
199
200 spin_unlock_irqrestore(lock: &zone->lock, flags);
201 if (mode == PB_ISOLATE_MODE_MEM_OFFLINE) {
202 /*
203 * printk() with zone->lock held will likely trigger a
204 * lockdep splat, so defer it here.
205 */
206 dump_page(page: unmovable, reason: "unmovable page");
207 }
208
209 return -EBUSY;
210}
211
212static void unset_migratetype_isolate(struct page *page)
213{
214 struct zone *zone;
215 unsigned long flags;
216 bool isolated_page = false;
217 unsigned int order;
218 struct page *buddy;
219
220 zone = page_zone(page);
221 spin_lock_irqsave(&zone->lock, flags);
222 if (!is_migrate_isolate_page(page))
223 goto out;
224
225 /*
226 * Because freepage with more than pageblock_order on isolated
227 * pageblock is restricted to merge due to freepage counting problem,
228 * it is possible that there is free buddy page.
229 * move_freepages_block() doesn't care of merge so we need other
230 * approach in order to merge them. Isolation and free will make
231 * these pages to be merged.
232 */
233 if (PageBuddy(page)) {
234 order = buddy_order(page);
235 if (order >= pageblock_order && order < MAX_PAGE_ORDER) {
236 buddy = find_buddy_page_pfn(page, page_to_pfn(page),
237 order, NULL);
238 if (buddy && !is_migrate_isolate_page(page: buddy)) {
239 isolated_page = !!__isolate_free_page(page, order);
240 /*
241 * Isolating a free page in an isolated pageblock
242 * is expected to always work as watermarks don't
243 * apply here.
244 */
245 VM_WARN_ON(!isolated_page);
246 }
247 }
248 }
249
250 /*
251 * If we isolate freepage with more than pageblock_order, there
252 * should be no freepage in the range, so we could avoid costly
253 * pageblock scanning for freepage moving.
254 *
255 * We didn't actually touch any of the isolated pages, so place them
256 * to the tail of the freelist. This is an optimization for memory
257 * onlining - just onlined memory won't immediately be considered for
258 * allocation.
259 */
260 if (!isolated_page) {
261 /*
262 * Isolating this block already succeeded, so this
263 * should not fail on zone boundaries.
264 */
265 WARN_ON_ONCE(!pageblock_unisolate_and_move_free_pages(zone, page));
266 } else {
267 clear_pageblock_isolate(page);
268 __putback_isolated_page(page, order, get_pageblock_migratetype(page));
269 }
270 zone->nr_isolate_pageblock--;
271out:
272 spin_unlock_irqrestore(lock: &zone->lock, flags);
273}
274
275static inline struct page *
276__first_valid_page(unsigned long pfn, unsigned long nr_pages)
277{
278 int i;
279
280 for (i = 0; i < nr_pages; i++) {
281 struct page *page;
282
283 page = pfn_to_online_page(pfn: pfn + i);
284 if (!page)
285 continue;
286 return page;
287 }
288 return NULL;
289}
290
291/**
292 * isolate_single_pageblock() -- tries to isolate a pageblock that might be
293 * within a free or in-use page.
294 * @boundary_pfn: pageblock-aligned pfn that a page might cross
295 * @mode: isolation mode
296 * @isolate_before: isolate the pageblock before the boundary_pfn
297 * @skip_isolation: the flag to skip the pageblock isolation in second
298 * isolate_single_pageblock()
299 *
300 * Free and in-use pages can be as big as MAX_PAGE_ORDER and contain more than one
301 * pageblock. When not all pageblocks within a page are isolated at the same
302 * time, free page accounting can go wrong. For example, in the case of
303 * MAX_PAGE_ORDER = pageblock_order + 1, a MAX_PAGE_ORDER page has two
304 * pagelbocks.
305 * [ MAX_PAGE_ORDER ]
306 * [ pageblock0 | pageblock1 ]
307 * When either pageblock is isolated, if it is a free page, the page is not
308 * split into separate migratetype lists, which is supposed to; if it is an
309 * in-use page and freed later, __free_one_page() does not split the free page
310 * either. The function handles this by splitting the free page or migrating
311 * the in-use page then splitting the free page.
312 */
313static int isolate_single_pageblock(unsigned long boundary_pfn,
314 enum pb_isolate_mode mode, bool isolate_before,
315 bool skip_isolation)
316{
317 unsigned long start_pfn;
318 unsigned long isolate_pageblock;
319 unsigned long pfn;
320 struct zone *zone;
321 int ret;
322
323 VM_BUG_ON(!pageblock_aligned(boundary_pfn));
324
325 if (isolate_before)
326 isolate_pageblock = boundary_pfn - pageblock_nr_pages;
327 else
328 isolate_pageblock = boundary_pfn;
329
330 /*
331 * scan at the beginning of MAX_ORDER_NR_PAGES aligned range to avoid
332 * only isolating a subset of pageblocks from a bigger than pageblock
333 * free or in-use page. Also make sure all to-be-isolated pageblocks
334 * are within the same zone.
335 */
336 zone = page_zone(pfn_to_page(isolate_pageblock));
337 start_pfn = max(ALIGN_DOWN(isolate_pageblock, MAX_ORDER_NR_PAGES),
338 zone->zone_start_pfn);
339
340 if (skip_isolation) {
341 VM_BUG_ON(!get_pageblock_isolate(pfn_to_page(isolate_pageblock)));
342 } else {
343 ret = set_migratetype_isolate(pfn_to_page(isolate_pageblock),
344 mode, start_pfn: isolate_pageblock,
345 end_pfn: isolate_pageblock + pageblock_nr_pages);
346
347 if (ret)
348 return ret;
349 }
350
351 /*
352 * Bail out early when the to-be-isolated pageblock does not form
353 * a free or in-use page across boundary_pfn:
354 *
355 * 1. isolate before boundary_pfn: the page after is not online
356 * 2. isolate after boundary_pfn: the page before is not online
357 *
358 * This also ensures correctness. Without it, when isolate after
359 * boundary_pfn and [start_pfn, boundary_pfn) are not online,
360 * __first_valid_page() will return unexpected NULL in the for loop
361 * below.
362 */
363 if (isolate_before) {
364 if (!pfn_to_online_page(pfn: boundary_pfn))
365 return 0;
366 } else {
367 if (!pfn_to_online_page(pfn: boundary_pfn - 1))
368 return 0;
369 }
370
371 for (pfn = start_pfn; pfn < boundary_pfn;) {
372 struct page *page = __first_valid_page(pfn, nr_pages: boundary_pfn - pfn);
373
374 VM_BUG_ON(!page);
375 pfn = page_to_pfn(page);
376
377 if (PageUnaccepted(page)) {
378 pfn += MAX_ORDER_NR_PAGES;
379 continue;
380 }
381
382 if (PageBuddy(page)) {
383 int order = buddy_order(page);
384
385 /* pageblock_isolate_and_move_free_pages() handled this */
386 VM_WARN_ON_ONCE(pfn + (1 << order) > boundary_pfn);
387
388 pfn += 1UL << order;
389 continue;
390 }
391
392 /*
393 * If a compound page is straddling our block, attempt
394 * to migrate it out of the way.
395 *
396 * We don't have to worry about this creating a large
397 * free page that straddles into our block: gigantic
398 * pages are freed as order-0 chunks, and LRU pages
399 * (currently) do not exceed pageblock_order.
400 *
401 * The block of interest has already been marked
402 * MIGRATE_ISOLATE above, so when migration is done it
403 * will free its pages onto the correct freelists.
404 */
405 if (PageCompound(page)) {
406 struct page *head = compound_head(page);
407 unsigned long head_pfn = page_to_pfn(head);
408 unsigned long nr_pages = compound_nr(page: head);
409
410 if (head_pfn + nr_pages <= boundary_pfn ||
411 PageHuge(page)) {
412 pfn = head_pfn + nr_pages;
413 continue;
414 }
415
416 /*
417 * These pages are movable too, but they're
418 * not expected to exceed pageblock_order.
419 *
420 * Let us know when they do, so we can add
421 * proper free and split handling for them.
422 */
423 VM_WARN_ON_ONCE_PAGE(PageLRU(page), page);
424 VM_WARN_ON_ONCE_PAGE(page_has_movable_ops(page), page);
425
426 goto failed;
427 }
428
429 pfn++;
430 }
431 return 0;
432failed:
433 /* restore the original migratetype */
434 if (!skip_isolation)
435 unset_migratetype_isolate(pfn_to_page(isolate_pageblock));
436 return -EBUSY;
437}
438
439/**
440 * start_isolate_page_range() - mark page range MIGRATE_ISOLATE
441 * @start_pfn: The first PFN of the range to be isolated.
442 * @end_pfn: The last PFN of the range to be isolated.
443 * @mode: isolation mode
444 *
445 * Making page-allocation-type to be MIGRATE_ISOLATE means free pages in
446 * the range will never be allocated. Any free pages and pages freed in the
447 * future will not be allocated again. If specified range includes migrate types
448 * other than MOVABLE or CMA, this will fail with -EBUSY. For isolating all
449 * pages in the range finally, the caller have to free all pages in the range.
450 * test_page_isolated() can be used for test it.
451 *
452 * The function first tries to isolate the pageblocks at the beginning and end
453 * of the range, since there might be pages across the range boundaries.
454 * Afterwards, it isolates the rest of the range.
455 *
456 * There is no high level synchronization mechanism that prevents two threads
457 * from trying to isolate overlapping ranges. If this happens, one thread
458 * will notice pageblocks in the overlapping range already set to isolate.
459 * This happens in set_migratetype_isolate, and set_migratetype_isolate
460 * returns an error. We then clean up by restoring the migration type on
461 * pageblocks we may have modified and return -EBUSY to caller. This
462 * prevents two threads from simultaneously working on overlapping ranges.
463 *
464 * Please note that there is no strong synchronization with the page allocator
465 * either. Pages might be freed while their page blocks are marked ISOLATED.
466 * A call to drain_all_pages() after isolation can flush most of them. However
467 * in some cases pages might still end up on pcp lists and that would allow
468 * for their allocation even when they are in fact isolated already. Depending
469 * on how strong of a guarantee the caller needs, zone_pcp_disable/enable()
470 * might be used to flush and disable pcplist before isolation and enable after
471 * unisolation.
472 *
473 * Return: 0 on success and -EBUSY if any part of range cannot be isolated.
474 */
475int start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
476 enum pb_isolate_mode mode)
477{
478 unsigned long pfn;
479 struct page *page;
480 /* isolation is done at page block granularity */
481 unsigned long isolate_start = pageblock_start_pfn(start_pfn);
482 unsigned long isolate_end = pageblock_align(end_pfn);
483 int ret;
484 bool skip_isolation = false;
485
486 /* isolate [isolate_start, isolate_start + pageblock_nr_pages) pageblock */
487 ret = isolate_single_pageblock(boundary_pfn: isolate_start, mode, isolate_before: false,
488 skip_isolation);
489 if (ret)
490 return ret;
491
492 if (isolate_start == isolate_end - pageblock_nr_pages)
493 skip_isolation = true;
494
495 /* isolate [isolate_end - pageblock_nr_pages, isolate_end) pageblock */
496 ret = isolate_single_pageblock(boundary_pfn: isolate_end, mode, isolate_before: true, skip_isolation);
497 if (ret) {
498 unset_migratetype_isolate(pfn_to_page(isolate_start));
499 return ret;
500 }
501
502 /* skip isolated pageblocks at the beginning and end */
503 for (pfn = isolate_start + pageblock_nr_pages;
504 pfn < isolate_end - pageblock_nr_pages;
505 pfn += pageblock_nr_pages) {
506 page = __first_valid_page(pfn, pageblock_nr_pages);
507 if (page && set_migratetype_isolate(page, mode, start_pfn,
508 end_pfn)) {
509 undo_isolate_page_range(start_pfn: isolate_start, end_pfn: pfn);
510 unset_migratetype_isolate(
511 pfn_to_page(isolate_end - pageblock_nr_pages));
512 return -EBUSY;
513 }
514 }
515 return 0;
516}
517
518/**
519 * undo_isolate_page_range - undo effects of start_isolate_page_range()
520 * @start_pfn: The first PFN of the isolated range
521 * @end_pfn: The last PFN of the isolated range
522 *
523 * This finds and unsets every MIGRATE_ISOLATE page block in the given range
524 */
525void undo_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn)
526{
527 unsigned long pfn;
528 struct page *page;
529 unsigned long isolate_start = pageblock_start_pfn(start_pfn);
530 unsigned long isolate_end = pageblock_align(end_pfn);
531
532 for (pfn = isolate_start;
533 pfn < isolate_end;
534 pfn += pageblock_nr_pages) {
535 page = __first_valid_page(pfn, pageblock_nr_pages);
536 if (!page || !is_migrate_isolate_page(page))
537 continue;
538 unset_migratetype_isolate(page);
539 }
540}
541/*
542 * Test all pages in the range is free(means isolated) or not.
543 * all pages in [start_pfn...end_pfn) must be in the same zone.
544 * zone->lock must be held before call this.
545 *
546 * Returns the last tested pfn.
547 */
548static unsigned long
549__test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn,
550 enum pb_isolate_mode mode)
551{
552 struct page *page;
553
554 while (pfn < end_pfn) {
555 page = pfn_to_page(pfn);
556 if (PageBuddy(page))
557 /*
558 * If the page is on a free list, it has to be on
559 * the correct MIGRATE_ISOLATE freelist. There is no
560 * simple way to verify that as VM_BUG_ON(), though.
561 */
562 pfn += 1 << buddy_order(page);
563 else if ((mode == PB_ISOLATE_MODE_MEM_OFFLINE) &&
564 PageHWPoison(page))
565 /* A HWPoisoned page cannot be also PageBuddy */
566 pfn++;
567 else if ((mode == PB_ISOLATE_MODE_MEM_OFFLINE) &&
568 PageOffline(page) && !page_count(page))
569 /*
570 * The responsible driver agreed to skip PageOffline()
571 * pages when offlining memory by dropping its
572 * reference in MEM_GOING_OFFLINE.
573 */
574 pfn++;
575 else
576 break;
577 }
578
579 return pfn;
580}
581
582/**
583 * test_pages_isolated - check if pageblocks in range are isolated
584 * @start_pfn: The first PFN of the isolated range
585 * @end_pfn: The first PFN *after* the isolated range
586 * @mode: Testing mode
587 *
588 * This tests if all in the specified range are free.
589 *
590 * If %PB_ISOLATE_MODE_MEM_OFFLINE specified in @mode, it will consider
591 * poisoned and offlined pages free as well.
592 *
593 * Caller must ensure the requested range doesn't span zones.
594 *
595 * Returns 0 if true, -EBUSY if one or more pages are in use.
596 */
597int test_pages_isolated(unsigned long start_pfn, unsigned long end_pfn,
598 enum pb_isolate_mode mode)
599{
600 unsigned long pfn, flags;
601 struct page *page;
602 struct zone *zone;
603 int ret;
604
605 /*
606 * Due to the deferred freeing of hugetlb folios, the hugepage folios may
607 * not immediately release to the buddy system. This can cause PageBuddy()
608 * to fail in __test_page_isolated_in_pageblock(). To ensure that the
609 * hugetlb folios are properly released back to the buddy system, we
610 * invoke the wait_for_freed_hugetlb_folios() function to wait for the
611 * release to complete.
612 */
613 wait_for_freed_hugetlb_folios();
614
615 /*
616 * Note: pageblock_nr_pages != MAX_PAGE_ORDER. Then, chunks of free
617 * pages are not aligned to pageblock_nr_pages.
618 * Then we just check migratetype first.
619 */
620 for (pfn = start_pfn; pfn < end_pfn; pfn += pageblock_nr_pages) {
621 page = __first_valid_page(pfn, pageblock_nr_pages);
622 if (page && !is_migrate_isolate_page(page))
623 break;
624 }
625 page = __first_valid_page(pfn: start_pfn, nr_pages: end_pfn - start_pfn);
626 if ((pfn < end_pfn) || !page) {
627 ret = -EBUSY;
628 goto out;
629 }
630
631 /* Check all pages are free or marked as ISOLATED */
632 zone = page_zone(page);
633 spin_lock_irqsave(&zone->lock, flags);
634 pfn = __test_page_isolated_in_pageblock(pfn: start_pfn, end_pfn, mode);
635 spin_unlock_irqrestore(lock: &zone->lock, flags);
636
637 ret = pfn < end_pfn ? -EBUSY : 0;
638
639out:
640 trace_test_pages_isolated(start_pfn, end_pfn, fin_pfn: pfn);
641
642 return ret;
643}
644

source code of linux/mm/page_isolation.c