1/* SPDX-License-Identifier: GPL-2.0 */
2#ifndef _LINUX_PAGE_REF_H
3#define _LINUX_PAGE_REF_H
4
5#include <linux/atomic.h>
6#include <linux/mm_types.h>
7#include <linux/page-flags.h>
8#include <linux/tracepoint-defs.h>
9
10DECLARE_TRACEPOINT(page_ref_set);
11DECLARE_TRACEPOINT(page_ref_mod);
12DECLARE_TRACEPOINT(page_ref_mod_and_test);
13DECLARE_TRACEPOINT(page_ref_mod_and_return);
14DECLARE_TRACEPOINT(page_ref_mod_unless);
15DECLARE_TRACEPOINT(page_ref_freeze);
16DECLARE_TRACEPOINT(page_ref_unfreeze);
17
18#ifdef CONFIG_DEBUG_PAGE_REF
19
20/*
21 * Ideally we would want to use the trace_<tracepoint>_enabled() helper
22 * functions. But due to include header file issues, that is not
23 * feasible. Instead we have to open code the static key functions.
24 *
25 * See trace_##name##_enabled(void) in include/linux/tracepoint.h
26 */
27#define page_ref_tracepoint_active(t) tracepoint_enabled(t)
28
29extern void __page_ref_set(struct page *page, int v);
30extern void __page_ref_mod(struct page *page, int v);
31extern void __page_ref_mod_and_test(struct page *page, int v, int ret);
32extern void __page_ref_mod_and_return(struct page *page, int v, int ret);
33extern void __page_ref_mod_unless(struct page *page, int v, int u);
34extern void __page_ref_freeze(struct page *page, int v, int ret);
35extern void __page_ref_unfreeze(struct page *page, int v);
36
37#else
38
39#define page_ref_tracepoint_active(t) false
40
41static inline void __page_ref_set(struct page *page, int v)
42{
43}
44static inline void __page_ref_mod(struct page *page, int v)
45{
46}
47static inline void __page_ref_mod_and_test(struct page *page, int v, int ret)
48{
49}
50static inline void __page_ref_mod_and_return(struct page *page, int v, int ret)
51{
52}
53static inline void __page_ref_mod_unless(struct page *page, int v, int u)
54{
55}
56static inline void __page_ref_freeze(struct page *page, int v, int ret)
57{
58}
59static inline void __page_ref_unfreeze(struct page *page, int v)
60{
61}
62
63#endif
64
65static inline int page_ref_count(const struct page *page)
66{
67 return atomic_read(v: &page->_refcount);
68}
69
70/**
71 * folio_ref_count - The reference count on this folio.
72 * @folio: The folio.
73 *
74 * The refcount is usually incremented by calls to folio_get() and
75 * decremented by calls to folio_put(). Some typical users of the
76 * folio refcount:
77 *
78 * - Each reference from a page table
79 * - The page cache
80 * - Filesystem private data
81 * - The LRU list
82 * - Pipes
83 * - Direct IO which references this page in the process address space
84 *
85 * Return: The number of references to this folio.
86 */
87static inline int folio_ref_count(const struct folio *folio)
88{
89 return page_ref_count(page: &folio->page);
90}
91
92static inline int page_count(const struct page *page)
93{
94 return folio_ref_count(page_folio(page));
95}
96
97static inline void set_page_count(struct page *page, int v)
98{
99 atomic_set(v: &page->_refcount, i: v);
100 if (page_ref_tracepoint_active(page_ref_set))
101 __page_ref_set(page, v);
102}
103
104static inline void folio_set_count(struct folio *folio, int v)
105{
106 set_page_count(page: &folio->page, v);
107}
108
109/*
110 * Setup the page count before being freed into the page allocator for
111 * the first time (boot or memory hotplug)
112 */
113static inline void init_page_count(struct page *page)
114{
115 set_page_count(page, v: 1);
116}
117
118static inline void page_ref_add(struct page *page, int nr)
119{
120 atomic_add(i: nr, v: &page->_refcount);
121 if (page_ref_tracepoint_active(page_ref_mod))
122 __page_ref_mod(page, v: nr);
123}
124
125static inline void folio_ref_add(struct folio *folio, int nr)
126{
127 page_ref_add(page: &folio->page, nr);
128}
129
130static inline void page_ref_sub(struct page *page, int nr)
131{
132 atomic_sub(i: nr, v: &page->_refcount);
133 if (page_ref_tracepoint_active(page_ref_mod))
134 __page_ref_mod(page, v: -nr);
135}
136
137static inline void folio_ref_sub(struct folio *folio, int nr)
138{
139 page_ref_sub(page: &folio->page, nr);
140}
141
142static inline int page_ref_sub_return(struct page *page, int nr)
143{
144 int ret = atomic_sub_return(i: nr, v: &page->_refcount);
145
146 if (page_ref_tracepoint_active(page_ref_mod_and_return))
147 __page_ref_mod_and_return(page, v: -nr, ret);
148 return ret;
149}
150
151static inline int folio_ref_sub_return(struct folio *folio, int nr)
152{
153 return page_ref_sub_return(page: &folio->page, nr);
154}
155
156static inline void page_ref_inc(struct page *page)
157{
158 atomic_inc(v: &page->_refcount);
159 if (page_ref_tracepoint_active(page_ref_mod))
160 __page_ref_mod(page, v: 1);
161}
162
163static inline void folio_ref_inc(struct folio *folio)
164{
165 page_ref_inc(page: &folio->page);
166}
167
168static inline void page_ref_dec(struct page *page)
169{
170 atomic_dec(v: &page->_refcount);
171 if (page_ref_tracepoint_active(page_ref_mod))
172 __page_ref_mod(page, v: -1);
173}
174
175static inline void folio_ref_dec(struct folio *folio)
176{
177 page_ref_dec(page: &folio->page);
178}
179
180static inline int page_ref_sub_and_test(struct page *page, int nr)
181{
182 int ret = atomic_sub_and_test(i: nr, v: &page->_refcount);
183
184 if (page_ref_tracepoint_active(page_ref_mod_and_test))
185 __page_ref_mod_and_test(page, v: -nr, ret);
186 return ret;
187}
188
189static inline int folio_ref_sub_and_test(struct folio *folio, int nr)
190{
191 return page_ref_sub_and_test(page: &folio->page, nr);
192}
193
194static inline int page_ref_inc_return(struct page *page)
195{
196 int ret = atomic_inc_return(v: &page->_refcount);
197
198 if (page_ref_tracepoint_active(page_ref_mod_and_return))
199 __page_ref_mod_and_return(page, v: 1, ret);
200 return ret;
201}
202
203static inline int folio_ref_inc_return(struct folio *folio)
204{
205 return page_ref_inc_return(page: &folio->page);
206}
207
208static inline int page_ref_dec_and_test(struct page *page)
209{
210 int ret = atomic_dec_and_test(v: &page->_refcount);
211
212 if (page_ref_tracepoint_active(page_ref_mod_and_test))
213 __page_ref_mod_and_test(page, v: -1, ret);
214 return ret;
215}
216
217static inline int folio_ref_dec_and_test(struct folio *folio)
218{
219 return page_ref_dec_and_test(page: &folio->page);
220}
221
222static inline int page_ref_dec_return(struct page *page)
223{
224 int ret = atomic_dec_return(v: &page->_refcount);
225
226 if (page_ref_tracepoint_active(page_ref_mod_and_return))
227 __page_ref_mod_and_return(page, v: -1, ret);
228 return ret;
229}
230
231static inline int folio_ref_dec_return(struct folio *folio)
232{
233 return page_ref_dec_return(page: &folio->page);
234}
235
236static inline bool page_ref_add_unless(struct page *page, int nr, int u)
237{
238 bool ret = atomic_add_unless(v: &page->_refcount, a: nr, u);
239
240 if (page_ref_tracepoint_active(page_ref_mod_unless))
241 __page_ref_mod_unless(page, v: nr, u: ret);
242 return ret;
243}
244
245static inline bool folio_ref_add_unless(struct folio *folio, int nr, int u)
246{
247 return page_ref_add_unless(page: &folio->page, nr, u);
248}
249
250/**
251 * folio_try_get - Attempt to increase the refcount on a folio.
252 * @folio: The folio.
253 *
254 * If you do not already have a reference to a folio, you can attempt to
255 * get one using this function. It may fail if, for example, the folio
256 * has been freed since you found a pointer to it, or it is frozen for
257 * the purposes of splitting or migration.
258 *
259 * Return: True if the reference count was successfully incremented.
260 */
261static inline bool folio_try_get(struct folio *folio)
262{
263 return folio_ref_add_unless(folio, nr: 1, u: 0);
264}
265
266static inline bool folio_ref_try_add_rcu(struct folio *folio, int count)
267{
268#ifdef CONFIG_TINY_RCU
269 /*
270 * The caller guarantees the folio will not be freed from interrupt
271 * context, so (on !SMP) we only need preemption to be disabled
272 * and TINY_RCU does that for us.
273 */
274# ifdef CONFIG_PREEMPT_COUNT
275 VM_BUG_ON(!in_atomic() && !irqs_disabled());
276# endif
277 VM_BUG_ON_FOLIO(folio_ref_count(folio) == 0, folio);
278 folio_ref_add(folio, count);
279#else
280 if (unlikely(!folio_ref_add_unless(folio, count, 0))) {
281 /* Either the folio has been freed, or will be freed. */
282 return false;
283 }
284#endif
285 return true;
286}
287
288/**
289 * folio_try_get_rcu - Attempt to increase the refcount on a folio.
290 * @folio: The folio.
291 *
292 * This is a version of folio_try_get() optimised for non-SMP kernels.
293 * If you are still holding the rcu_read_lock() after looking up the
294 * page and know that the page cannot have its refcount decreased to
295 * zero in interrupt context, you can use this instead of folio_try_get().
296 *
297 * Example users include get_user_pages_fast() (as pages are not unmapped
298 * from interrupt context) and the page cache lookups (as pages are not
299 * truncated from interrupt context). We also know that pages are not
300 * frozen in interrupt context for the purposes of splitting or migration.
301 *
302 * You can also use this function if you're holding a lock that prevents
303 * pages being frozen & removed; eg the i_pages lock for the page cache
304 * or the mmap_lock or page table lock for page tables. In this case,
305 * it will always succeed, and you could have used a plain folio_get(),
306 * but it's sometimes more convenient to have a common function called
307 * from both locked and RCU-protected contexts.
308 *
309 * Return: True if the reference count was successfully incremented.
310 */
311static inline bool folio_try_get_rcu(struct folio *folio)
312{
313 return folio_ref_try_add_rcu(folio, count: 1);
314}
315
316static inline int page_ref_freeze(struct page *page, int count)
317{
318 int ret = likely(atomic_cmpxchg(&page->_refcount, count, 0) == count);
319
320 if (page_ref_tracepoint_active(page_ref_freeze))
321 __page_ref_freeze(page, v: count, ret);
322 return ret;
323}
324
325static inline int folio_ref_freeze(struct folio *folio, int count)
326{
327 return page_ref_freeze(page: &folio->page, count);
328}
329
330static inline void page_ref_unfreeze(struct page *page, int count)
331{
332 VM_BUG_ON_PAGE(page_count(page) != 0, page);
333 VM_BUG_ON(count == 0);
334
335 atomic_set_release(v: &page->_refcount, i: count);
336 if (page_ref_tracepoint_active(page_ref_unfreeze))
337 __page_ref_unfreeze(page, v: count);
338}
339
340static inline void folio_ref_unfreeze(struct folio *folio, int count)
341{
342 page_ref_unfreeze(page: &folio->page, count);
343}
344#endif
345

source code of linux/include/linux/page_ref.h