Line data Source code
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 :
10 : DECLARE_TRACEPOINT(page_ref_set);
11 : DECLARE_TRACEPOINT(page_ref_mod);
12 : DECLARE_TRACEPOINT(page_ref_mod_and_test);
13 : DECLARE_TRACEPOINT(page_ref_mod_and_return);
14 : DECLARE_TRACEPOINT(page_ref_mod_unless);
15 : DECLARE_TRACEPOINT(page_ref_freeze);
16 : DECLARE_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 :
29 : extern void __page_ref_set(struct page *page, int v);
30 : extern void __page_ref_mod(struct page *page, int v);
31 : extern void __page_ref_mod_and_test(struct page *page, int v, int ret);
32 : extern void __page_ref_mod_and_return(struct page *page, int v, int ret);
33 : extern void __page_ref_mod_unless(struct page *page, int v, int u);
34 : extern void __page_ref_freeze(struct page *page, int v, int ret);
35 : extern void __page_ref_unfreeze(struct page *page, int v);
36 :
37 : #else
38 :
39 : #define page_ref_tracepoint_active(t) false
40 :
41 : static inline void __page_ref_set(struct page *page, int v)
42 : {
43 : }
44 : static inline void __page_ref_mod(struct page *page, int v)
45 : {
46 : }
47 : static inline void __page_ref_mod_and_test(struct page *page, int v, int ret)
48 : {
49 : }
50 : static inline void __page_ref_mod_and_return(struct page *page, int v, int ret)
51 : {
52 : }
53 : static inline void __page_ref_mod_unless(struct page *page, int v, int u)
54 : {
55 : }
56 : static inline void __page_ref_freeze(struct page *page, int v, int ret)
57 : {
58 : }
59 : static inline void __page_ref_unfreeze(struct page *page, int v)
60 : {
61 : }
62 :
63 : #endif
64 :
65 : static inline int page_ref_count(const struct page *page)
66 : {
67 516096 : return atomic_read(&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 : */
87 : static inline int folio_ref_count(const struct folio *folio)
88 : {
89 0 : return page_ref_count(&folio->page);
90 : }
91 :
92 : static inline int page_count(const struct page *page)
93 : {
94 0 : return folio_ref_count(page_folio(page));
95 : }
96 :
97 : static inline void set_page_count(struct page *page, int v)
98 : {
99 1139490 : atomic_set(&page->_refcount, v);
100 : if (page_ref_tracepoint_active(page_ref_set))
101 : __page_ref_set(page, v);
102 : }
103 :
104 : static inline void folio_set_count(struct folio *folio, int v)
105 : {
106 : set_page_count(&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 : */
113 : static inline void init_page_count(struct page *page)
114 : {
115 270239 : set_page_count(page, 1);
116 : }
117 :
118 : static inline void page_ref_add(struct page *page, int nr)
119 : {
120 0 : atomic_add(nr, &page->_refcount);
121 : if (page_ref_tracepoint_active(page_ref_mod))
122 : __page_ref_mod(page, nr);
123 : }
124 :
125 : static inline void folio_ref_add(struct folio *folio, int nr)
126 : {
127 0 : page_ref_add(&folio->page, nr);
128 : }
129 :
130 : static inline void page_ref_sub(struct page *page, int nr)
131 : {
132 0 : atomic_sub(nr, &page->_refcount);
133 : if (page_ref_tracepoint_active(page_ref_mod))
134 : __page_ref_mod(page, -nr);
135 : }
136 :
137 : static inline void folio_ref_sub(struct folio *folio, int nr)
138 : {
139 0 : page_ref_sub(&folio->page, nr);
140 : }
141 :
142 : static inline int page_ref_sub_return(struct page *page, int nr)
143 : {
144 : int ret = atomic_sub_return(nr, &page->_refcount);
145 :
146 : if (page_ref_tracepoint_active(page_ref_mod_and_return))
147 : __page_ref_mod_and_return(page, -nr, ret);
148 : return ret;
149 : }
150 :
151 : static inline int folio_ref_sub_return(struct folio *folio, int nr)
152 : {
153 : return page_ref_sub_return(&folio->page, nr);
154 : }
155 :
156 : static inline void page_ref_inc(struct page *page)
157 : {
158 0 : atomic_inc(&page->_refcount);
159 : if (page_ref_tracepoint_active(page_ref_mod))
160 : __page_ref_mod(page, 1);
161 : }
162 :
163 : static inline void folio_ref_inc(struct folio *folio)
164 : {
165 0 : page_ref_inc(&folio->page);
166 : }
167 :
168 : static inline void page_ref_dec(struct page *page)
169 : {
170 : atomic_dec(&page->_refcount);
171 : if (page_ref_tracepoint_active(page_ref_mod))
172 : __page_ref_mod(page, -1);
173 : }
174 :
175 : static inline void folio_ref_dec(struct folio *folio)
176 : {
177 : page_ref_dec(&folio->page);
178 : }
179 :
180 : static inline int page_ref_sub_and_test(struct page *page, int nr)
181 : {
182 0 : int ret = atomic_sub_and_test(nr, &page->_refcount);
183 :
184 : if (page_ref_tracepoint_active(page_ref_mod_and_test))
185 : __page_ref_mod_and_test(page, -nr, ret);
186 : return ret;
187 : }
188 :
189 : static inline int folio_ref_sub_and_test(struct folio *folio, int nr)
190 : {
191 0 : return page_ref_sub_and_test(&folio->page, nr);
192 : }
193 :
194 : static inline int page_ref_inc_return(struct page *page)
195 : {
196 : int ret = atomic_inc_return(&page->_refcount);
197 :
198 : if (page_ref_tracepoint_active(page_ref_mod_and_return))
199 : __page_ref_mod_and_return(page, 1, ret);
200 : return ret;
201 : }
202 :
203 : static inline int folio_ref_inc_return(struct folio *folio)
204 : {
205 : return page_ref_inc_return(&folio->page);
206 : }
207 :
208 : static inline int page_ref_dec_and_test(struct page *page)
209 : {
210 89078 : int ret = atomic_dec_and_test(&page->_refcount);
211 :
212 : if (page_ref_tracepoint_active(page_ref_mod_and_test))
213 : __page_ref_mod_and_test(page, -1, ret);
214 : return ret;
215 : }
216 :
217 : static inline int folio_ref_dec_and_test(struct folio *folio)
218 : {
219 : return page_ref_dec_and_test(&folio->page);
220 : }
221 :
222 : static inline int page_ref_dec_return(struct page *page)
223 : {
224 : int ret = atomic_dec_return(&page->_refcount);
225 :
226 : if (page_ref_tracepoint_active(page_ref_mod_and_return))
227 : __page_ref_mod_and_return(page, -1, ret);
228 : return ret;
229 : }
230 :
231 : static inline int folio_ref_dec_return(struct folio *folio)
232 : {
233 : return page_ref_dec_return(&folio->page);
234 : }
235 :
236 : static inline bool page_ref_add_unless(struct page *page, int nr, int u)
237 : {
238 0 : bool ret = atomic_add_unless(&page->_refcount, nr, u);
239 :
240 : if (page_ref_tracepoint_active(page_ref_mod_unless))
241 : __page_ref_mod_unless(page, nr, ret);
242 : return ret;
243 : }
244 :
245 : static inline bool folio_ref_add_unless(struct folio *folio, int nr, int u)
246 : {
247 0 : return page_ref_add_unless(&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 : */
261 : static inline bool folio_try_get(struct folio *folio)
262 : {
263 0 : return folio_ref_add_unless(folio, 1, 0);
264 : }
265 :
266 : static 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 0 : 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 : */
311 : static inline bool folio_try_get_rcu(struct folio *folio)
312 : {
313 0 : return folio_ref_try_add_rcu(folio, 1);
314 : }
315 :
316 : static inline int page_ref_freeze(struct page *page, int count)
317 : {
318 0 : 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, count, ret);
322 : return ret;
323 : }
324 :
325 : static inline int folio_ref_freeze(struct folio *folio, int count)
326 : {
327 0 : return page_ref_freeze(&folio->page, count);
328 : }
329 :
330 : static 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 0 : atomic_set_release(&page->_refcount, count);
336 : if (page_ref_tracepoint_active(page_ref_unfreeze))
337 : __page_ref_unfreeze(page, count);
338 : }
339 :
340 : static inline void folio_ref_unfreeze(struct folio *folio, int count)
341 : {
342 0 : page_ref_unfreeze(&folio->page, count);
343 : }
344 : #endif
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