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 
__page_ref_set(struct page * page,int v)41 static inline void __page_ref_set(struct page *page, int v)
42 {
43 }
__page_ref_mod(struct page * page,int v)44 static inline void __page_ref_mod(struct page *page, int v)
45 {
46 }
__page_ref_mod_and_test(struct page * page,int v,int ret)47 static inline void __page_ref_mod_and_test(struct page *page, int v, int ret)
48 {
49 }
__page_ref_mod_and_return(struct page * page,int v,int ret)50 static inline void __page_ref_mod_and_return(struct page *page, int v, int ret)
51 {
52 }
__page_ref_mod_unless(struct page * page,int v,int u)53 static inline void __page_ref_mod_unless(struct page *page, int v, int u)
54 {
55 }
__page_ref_freeze(struct page * page,int v,int ret)56 static inline void __page_ref_freeze(struct page *page, int v, int ret)
57 {
58 }
__page_ref_unfreeze(struct page * page,int v)59 static inline void __page_ref_unfreeze(struct page *page, int v)
60 {
61 }
62 
63 #endif
64 
page_ref_count(const struct page * page)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  */
folio_ref_count(const struct folio * folio)87 static inline int folio_ref_count(const struct folio *folio)
88 {
89 	return page_ref_count(&folio->page);
90 }
91 
page_count(const struct page * page)92 static inline int page_count(const struct page *page)
93 {
94 	return folio_ref_count(page_folio(page));
95 }
96 
set_page_count(struct page * page,int v)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 
folio_set_count(struct folio * folio,int v)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  */
init_page_count(struct page * page)113 static inline void init_page_count(struct page *page)
114 {
115 	set_page_count(page, 1);
116 }
117 
page_ref_add(struct page * page,int nr)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 
folio_ref_add(struct folio * folio,int nr)125 static inline void folio_ref_add(struct folio *folio, int nr)
126 {
127 	page_ref_add(&folio->page, nr);
128 }
129 
page_ref_sub(struct page * page,int nr)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 
folio_ref_sub(struct folio * folio,int nr)137 static inline void folio_ref_sub(struct folio *folio, int nr)
138 {
139 	page_ref_sub(&folio->page, nr);
140 }
141 
page_ref_sub_return(struct page * page,int nr)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 
folio_ref_sub_return(struct folio * folio,int nr)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 
page_ref_inc(struct page * page)156 static inline void page_ref_inc(struct page *page)
157 {
158 	atomic_inc(&page->_refcount);
159 	if (page_ref_tracepoint_active(page_ref_mod))
160 		__page_ref_mod(page, 1);
161 }
162 
folio_ref_inc(struct folio * folio)163 static inline void folio_ref_inc(struct folio *folio)
164 {
165 	page_ref_inc(&folio->page);
166 }
167 
page_ref_dec(struct page * page)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 
folio_ref_dec(struct folio * folio)175 static inline void folio_ref_dec(struct folio *folio)
176 {
177 	page_ref_dec(&folio->page);
178 }
179 
page_ref_sub_and_test(struct page * page,int nr)180 static inline int page_ref_sub_and_test(struct page *page, int nr)
181 {
182 	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 
folio_ref_sub_and_test(struct folio * folio,int nr)189 static inline int folio_ref_sub_and_test(struct folio *folio, int nr)
190 {
191 	return page_ref_sub_and_test(&folio->page, nr);
192 }
193 
page_ref_inc_return(struct page * page)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 
folio_ref_inc_return(struct folio * folio)203 static inline int folio_ref_inc_return(struct folio *folio)
204 {
205 	return page_ref_inc_return(&folio->page);
206 }
207 
page_ref_dec_and_test(struct page * page)208 static inline int page_ref_dec_and_test(struct page *page)
209 {
210 	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 
folio_ref_dec_and_test(struct folio * folio)217 static inline int folio_ref_dec_and_test(struct folio *folio)
218 {
219 	return page_ref_dec_and_test(&folio->page);
220 }
221 
page_ref_dec_return(struct page * page)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 
folio_ref_dec_return(struct folio * folio)231 static inline int folio_ref_dec_return(struct folio *folio)
232 {
233 	return page_ref_dec_return(&folio->page);
234 }
235 
page_ref_add_unless(struct page * page,int nr,int u)236 static inline bool page_ref_add_unless(struct page *page, int nr, int u)
237 {
238 	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 
folio_ref_add_unless(struct folio * folio,int nr,int u)245 static inline bool folio_ref_add_unless(struct folio *folio, int nr, int u)
246 {
247 	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  */
folio_try_get(struct folio * folio)261 static inline bool folio_try_get(struct folio *folio)
262 {
263 	return folio_ref_add_unless(folio, 1, 0);
264 }
265 
folio_ref_try_add_rcu(struct folio * folio,int count)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 	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  */
folio_try_get_rcu(struct folio * folio)311 static inline bool folio_try_get_rcu(struct folio *folio)
312 {
313 	return folio_ref_try_add_rcu(folio, 1);
314 }
315 
page_ref_freeze(struct page * page,int count)316 static 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, count, ret);
322 	return ret;
323 }
324 
folio_ref_freeze(struct folio * folio,int count)325 static inline int folio_ref_freeze(struct folio *folio, int count)
326 {
327 	return page_ref_freeze(&folio->page, count);
328 }
329 
page_ref_unfreeze(struct page * page,int count)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 	atomic_set_release(&page->_refcount, count);
336 	if (page_ref_tracepoint_active(page_ref_unfreeze))
337 		__page_ref_unfreeze(page, count);
338 }
339 
folio_ref_unfreeze(struct folio * folio,int count)340 static inline void folio_ref_unfreeze(struct folio *folio, int count)
341 {
342 	page_ref_unfreeze(&folio->page, count);
343 }
344 #endif
345