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 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 return page_ref_count(&folio->page);
90 }
91
92 static inline int page_count(const struct page *page)
93 {
94 return folio_ref_count(page_folio(page));
95 }
96
97 static inline void set_page_count(struct page *page, int v)
98 {
99 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 set_page_count(page, 1);
116 }
117
118 static inline void page_ref_add(struct page *page, int nr)
119 {
120 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 page_ref_add(&folio->page, nr);
128 }
129
130 static inline void page_ref_sub(struct page *page, int nr)
131 {
132 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 page_ref_sub(&folio->page, nr);
140 }
141
142 static inline int folio_ref_sub_return(struct folio *folio, int nr)
143 {
144 int ret = atomic_sub_return(nr, &folio->_refcount);
145
146 if (page_ref_tracepoint_active(page_ref_mod_and_return))
147 __page_ref_mod_and_return(&folio->page, -nr, ret);
148 return ret;
149 }
150
151 static inline void page_ref_inc(struct page *page)
152 {
153 atomic_inc(&page->_refcount);
154 if (page_ref_tracepoint_active(page_ref_mod))
155 __page_ref_mod(page, 1);
156 }
157
158 static inline void folio_ref_inc(struct folio *folio)
159 {
160 page_ref_inc(&folio->page);
161 }
162
163 static inline void page_ref_dec(struct page *page)
164 {
165 atomic_dec(&page->_refcount);
166 if (page_ref_tracepoint_active(page_ref_mod))
167 __page_ref_mod(page, -1);
168 }
169
170 static inline void folio_ref_dec(struct folio *folio)
171 {
172 page_ref_dec(&folio->page);
173 }
174
175 static inline int page_ref_sub_and_test(struct page *page, int nr)
176 {
177 int ret = atomic_sub_and_test(nr, &page->_refcount);
178
179 if (page_ref_tracepoint_active(page_ref_mod_and_test))
180 __page_ref_mod_and_test(page, -nr, ret);
181 return ret;
182 }
183
184 static inline int folio_ref_sub_and_test(struct folio *folio, int nr)
185 {
186 return page_ref_sub_and_test(&folio->page, nr);
187 }
188
189 static inline int page_ref_inc_return(struct page *page)
190 {
191 int ret = atomic_inc_return(&page->_refcount);
192
193 if (page_ref_tracepoint_active(page_ref_mod_and_return))
194 __page_ref_mod_and_return(page, 1, ret);
195 return ret;
196 }
197
198 static inline int folio_ref_inc_return(struct folio *folio)
199 {
200 return page_ref_inc_return(&folio->page);
201 }
202
203 static inline int page_ref_dec_and_test(struct page *page)
204 {
205 int ret = atomic_dec_and_test(&page->_refcount);
206
207 if (page_ref_tracepoint_active(page_ref_mod_and_test))
208 __page_ref_mod_and_test(page, -1, ret);
209 return ret;
210 }
211
212 static inline int folio_ref_dec_and_test(struct folio *folio)
213 {
214 return page_ref_dec_and_test(&folio->page);
215 }
216
217 static inline int page_ref_dec_return(struct page *page)
218 {
219 int ret = atomic_dec_return(&page->_refcount);
220
221 if (page_ref_tracepoint_active(page_ref_mod_and_return))
222 __page_ref_mod_and_return(page, -1, ret);
223 return ret;
224 }
225
226 static inline int folio_ref_dec_return(struct folio *folio)
227 {
228 return page_ref_dec_return(&folio->page);
229 }
230
231 static 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_is_fake_head(page) && page_ref_count(page) != u)
238 ret = atomic_add_unless(&page->_refcount, nr, u);
239 rcu_read_unlock();
240
241 if (page_ref_tracepoint_active(page_ref_mod_unless))
242 __page_ref_mod_unless(page, nr, ret);
243 return ret;
244 }
245
246 static inline bool folio_ref_add_unless(struct folio *folio, int nr, int u)
247 {
248 return page_ref_add_unless(&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 */
262 static inline bool folio_try_get(struct folio *folio)
263 {
264 return folio_ref_add_unless(folio, 1, 0);
265 }
266
267 static inline bool folio_ref_try_add(struct folio *folio, int count)
268 {
269 return folio_ref_add_unless(folio, count, 0);
270 }
271
272 static 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, count, ret);
278 return ret;
279 }
280
281 static inline int folio_ref_freeze(struct folio *folio, int count)
282 {
283 return page_ref_freeze(&folio->page, count);
284 }
285
286 static 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(&page->_refcount, count);
292 if (page_ref_tracepoint_active(page_ref_unfreeze))
293 __page_ref_unfreeze(page, count);
294 }
295
296 static inline void folio_ref_unfreeze(struct folio *folio, int count)
297 {
298 page_ref_unfreeze(&folio->page, count);
299 }
300 #endif
301
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