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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 folio_ref_sub_return(struct folio *folio, int nr)
143{
144 int ret = atomic_sub_return(i: nr, v: &folio->_refcount);
145
146 if (page_ref_tracepoint_active(page_ref_mod_and_return))
147 __page_ref_mod_and_return(page: &folio->page, v: -nr, ret);
148 return ret;
149}
150
151static inline void page_ref_inc(struct page *page)
152{
153 atomic_inc(v: &page->_refcount);
154 if (page_ref_tracepoint_active(page_ref_mod))
155 __page_ref_mod(page, v: 1);
156}
157
158static inline void folio_ref_inc(struct folio *folio)
159{
160 page_ref_inc(page: &folio->page);
161}
162
163static inline void page_ref_dec(struct page *page)
164{
165 atomic_dec(v: &page->_refcount);
166 if (page_ref_tracepoint_active(page_ref_mod))
167 __page_ref_mod(page, v: -1);
168}
169
170static inline void folio_ref_dec(struct folio *folio)
171{
172 page_ref_dec(page: &folio->page);
173}
174
175static inline int page_ref_sub_and_test(struct page *page, int nr)
176{
177 int ret = atomic_sub_and_test(i: nr, v: &page->_refcount);
178
179 if (page_ref_tracepoint_active(page_ref_mod_and_test))
180 __page_ref_mod_and_test(page, v: -nr, ret);
181 return ret;
182}
183
184static inline int folio_ref_sub_and_test(struct folio *folio, int nr)
185{
186 return page_ref_sub_and_test(page: &folio->page, nr);
187}
188
189static inline int page_ref_inc_return(struct page *page)
190{
191 int ret = atomic_inc_return(v: &page->_refcount);
192
193 if (page_ref_tracepoint_active(page_ref_mod_and_return))
194 __page_ref_mod_and_return(page, v: 1, ret);
195 return ret;
196}
197
198static inline int folio_ref_inc_return(struct folio *folio)
199{
200 return page_ref_inc_return(page: &folio->page);
201}
202
203static inline int page_ref_dec_and_test(struct page *page)
204{
205 int ret = atomic_dec_and_test(v: &page->_refcount);
206
207 if (page_ref_tracepoint_active(page_ref_mod_and_test))
208 __page_ref_mod_and_test(page, v: -1, ret);
209 return ret;
210}
211
212static inline int folio_ref_dec_and_test(struct folio *folio)
213{
214 return page_ref_dec_and_test(page: &folio->page);
215}
216
217static inline int page_ref_dec_return(struct page *page)
218{
219 int ret = atomic_dec_return(v: &page->_refcount);
220
221 if (page_ref_tracepoint_active(page_ref_mod_and_return))
222 __page_ref_mod_and_return(page, v: -1, ret);
223 return ret;
224}
225
226static inline int folio_ref_dec_return(struct folio *folio)
227{
228 return page_ref_dec_return(page: &folio->page);
229}
230
231static inline bool page_ref_add_unless(struct page *page, int nr, int u)
232{
233 bool ret = false;
234
235 rcu_read_lock();
236 /* avoid writing to the vmemmap area being remapped */
237 if (page_count_writable(page, u))
238 ret = atomic_add_unless(v: &page->_refcount, a: nr, u);
239 rcu_read_unlock();
240
241 if (page_ref_tracepoint_active(page_ref_mod_unless))
242 __page_ref_mod_unless(page, v: nr, u: ret);
243 return ret;
244}
245
246static inline bool folio_ref_add_unless(struct folio *folio, int nr, int u)
247{
248 return page_ref_add_unless(page: &folio->page, nr, u);
249}
250
251/**
252 * folio_try_get - Attempt to increase the refcount on a folio.
253 * @folio: The folio.
254 *
255 * If you do not already have a reference to a folio, you can attempt to
256 * get one using this function. It may fail if, for example, the folio
257 * has been freed since you found a pointer to it, or it is frozen for
258 * the purposes of splitting or migration.
259 *
260 * Return: True if the reference count was successfully incremented.
261 */
262static inline bool folio_try_get(struct folio *folio)
263{
264 return folio_ref_add_unless(folio, nr: 1, u: 0);
265}
266
267static inline bool folio_ref_try_add(struct folio *folio, int count)
268{
269 return folio_ref_add_unless(folio, nr: count, u: 0);
270}
271
272static inline int page_ref_freeze(struct page *page, int count)
273{
274 int ret = likely(atomic_cmpxchg(&page->_refcount, count, 0) == count);
275
276 if (page_ref_tracepoint_active(page_ref_freeze))
277 __page_ref_freeze(page, v: count, ret);
278 return ret;
279}
280
281static inline int folio_ref_freeze(struct folio *folio, int count)
282{
283 return page_ref_freeze(page: &folio->page, count);
284}
285
286static inline void page_ref_unfreeze(struct page *page, int count)
287{
288 VM_BUG_ON_PAGE(page_count(page) != 0, page);
289 VM_BUG_ON(count == 0);
290
291 atomic_set_release(v: &page->_refcount, i: count);
292 if (page_ref_tracepoint_active(page_ref_unfreeze))
293 __page_ref_unfreeze(page, v: count);
294}
295
296static inline void folio_ref_unfreeze(struct folio *folio, int count)
297{
298 page_ref_unfreeze(page: &folio->page, count);
299}
300#endif
301

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