include/linux/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
  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