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 = atomic_add_unless(&page->_refcount, nr, u); 234 235 if (page_ref_tracepoint_active(page_ref_mod_unless)) 236 __page_ref_mod_unless(page, nr, ret); 237 return ret; 238 } 239 240 static inline bool folio_ref_add_unless(struct folio *folio, int nr, int u) 241 { 242 return page_ref_add_unless(&folio->page, nr, u); 243 } 244 245 /** 246 * folio_try_get - Attempt to increase the refcount on a folio. 247 * @folio: The folio. 248 * 249 * If you do not already have a reference to a folio, you can attempt to 250 * get one using this function. It may fail if, for example, the folio 251 * has been freed since you found a pointer to it, or it is frozen for 252 * the purposes of splitting or migration. 253 * 254 * Return: True if the reference count was successfully incremented. 255 */ 256 static inline bool folio_try_get(struct folio *folio) 257 { 258 return folio_ref_add_unless(folio, 1, 0); 259 } 260 261 static inline bool folio_ref_try_add_rcu(struct folio *folio, int count) 262 { 263 #ifdef CONFIG_TINY_RCU 264 /* 265 * The caller guarantees the folio will not be freed from interrupt 266 * context, so (on !SMP) we only need preemption to be disabled 267 * and TINY_RCU does that for us. 268 */ 269 # ifdef CONFIG_PREEMPT_COUNT 270 VM_BUG_ON(!in_atomic() && !irqs_disabled()); 271 # endif 272 VM_BUG_ON_FOLIO(folio_ref_count(folio) == 0, folio); 273 folio_ref_add(folio, count); 274 #else 275 if (unlikely(!folio_ref_add_unless(folio, count, 0))) { 276 /* Either the folio has been freed, or will be freed. */ 277 return false; 278 } 279 #endif 280 return true; 281 } 282 283 /** 284 * folio_try_get_rcu - Attempt to increase the refcount on a folio. 285 * @folio: The folio. 286 * 287 * This is a version of folio_try_get() optimised for non-SMP kernels. 288 * If you are still holding the rcu_read_lock() after looking up the 289 * page and know that the page cannot have its refcount decreased to 290 * zero in interrupt context, you can use this instead of folio_try_get(). 291 * 292 * Example users include get_user_pages_fast() (as pages are not unmapped 293 * from interrupt context) and the page cache lookups (as pages are not 294 * truncated from interrupt context). We also know that pages are not 295 * frozen in interrupt context for the purposes of splitting or migration. 296 * 297 * You can also use this function if you're holding a lock that prevents 298 * pages being frozen & removed; eg the i_pages lock for the page cache 299 * or the mmap_lock or page table lock for page tables. In this case, 300 * it will always succeed, and you could have used a plain folio_get(), 301 * but it's sometimes more convenient to have a common function called 302 * from both locked and RCU-protected contexts. 303 * 304 * Return: True if the reference count was successfully incremented. 305 */ 306 static inline bool folio_try_get_rcu(struct folio *folio) 307 { 308 return folio_ref_try_add_rcu(folio, 1); 309 } 310 311 static inline int page_ref_freeze(struct page *page, int count) 312 { 313 int ret = likely(atomic_cmpxchg(&page->_refcount, count, 0) == count); 314 315 if (page_ref_tracepoint_active(page_ref_freeze)) 316 __page_ref_freeze(page, count, ret); 317 return ret; 318 } 319 320 static inline int folio_ref_freeze(struct folio *folio, int count) 321 { 322 return page_ref_freeze(&folio->page, count); 323 } 324 325 static inline void page_ref_unfreeze(struct page *page, int count) 326 { 327 VM_BUG_ON_PAGE(page_count(page) != 0, page); 328 VM_BUG_ON(count == 0); 329 330 atomic_set_release(&page->_refcount, count); 331 if (page_ref_tracepoint_active(page_ref_unfreeze)) 332 __page_ref_unfreeze(page, count); 333 } 334 335 static inline void folio_ref_unfreeze(struct folio *folio, int count) 336 { 337 page_ref_unfreeze(&folio->page, count); 338 } 339 #endif 340