page_ref.h

  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(&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(&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(&page->_refcount, 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(&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, 1);
116}
117
118static 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
125static inline void folio_ref_add(struct folio *folio, int nr)
126{
127	page_ref_add(&folio->page, nr);
128}
129
130static 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
137static inline void folio_ref_sub(struct folio *folio, int nr)
138{
139	page_ref_sub(&folio->page, nr);
140}
141
142static 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
151static 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
158static inline void folio_ref_inc(struct folio *folio)
159{
160	page_ref_inc(&folio->page);
161}
162
163static 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
170static inline void folio_ref_dec(struct folio *folio)
171{
172	page_ref_dec(&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(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
184static 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
189static 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
198static inline int folio_ref_inc_return(struct folio *folio)
199{
200	return page_ref_inc_return(&folio->page);
201}
202
203static 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
212static inline int folio_ref_dec_and_test(struct folio *folio)
213{
214	return page_ref_dec_and_test(&folio->page);
215}
216
217static 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
226static inline int folio_ref_dec_return(struct folio *folio)
227{
228	return page_ref_dec_return(&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(&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
246static 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 */
262static inline bool folio_try_get(struct folio *folio)
263{
264	return folio_ref_add_unless(folio, 1, 0);
265}
266
267static inline bool folio_ref_try_add(struct folio *folio, int count)
268{
269	return folio_ref_add_unless(folio, count, 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, count, ret);
278	return ret;
279}
280
281static inline int folio_ref_freeze(struct folio *folio, int count)
282{
283	return page_ref_freeze(&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(&page->_refcount, count);
292	if (page_ref_tracepoint_active(page_ref_unfreeze))
293		__page_ref_unfreeze(page, count);
294}
295
296static inline void folio_ref_unfreeze(struct folio *folio, int count)
297{
298	page_ref_unfreeze(&folio->page, count);
299}
300#endif