swap_state.c revision bd53b714d32a29bdf33009f812e295667e92b930
1/* 2 * linux/mm/swap_state.c 3 * 4 * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds 5 * Swap reorganised 29.12.95, Stephen Tweedie 6 * 7 * Rewritten to use page cache, (C) 1998 Stephen Tweedie 8 */ 9#include <linux/module.h> 10#include <linux/mm.h> 11#include <linux/kernel_stat.h> 12#include <linux/swap.h> 13#include <linux/init.h> 14#include <linux/pagemap.h> 15#include <linux/buffer_head.h> 16#include <linux/backing-dev.h> 17 18#include <asm/pgtable.h> 19 20/* 21 * swapper_space is a fiction, retained to simplify the path through 22 * vmscan's shrink_list, to make sync_page look nicer, and to allow 23 * future use of radix_tree tags in the swap cache. 24 */ 25static struct address_space_operations swap_aops = { 26 .writepage = swap_writepage, 27 .sync_page = block_sync_page, 28 .set_page_dirty = __set_page_dirty_nobuffers, 29}; 30 31static struct backing_dev_info swap_backing_dev_info = { 32 .capabilities = BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK, 33 .unplug_io_fn = swap_unplug_io_fn, 34}; 35 36struct address_space swapper_space = { 37 .page_tree = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN), 38 .tree_lock = RW_LOCK_UNLOCKED, 39 .a_ops = &swap_aops, 40 .i_mmap_nonlinear = LIST_HEAD_INIT(swapper_space.i_mmap_nonlinear), 41 .backing_dev_info = &swap_backing_dev_info, 42}; 43EXPORT_SYMBOL(swapper_space); 44 45#define INC_CACHE_INFO(x) do { swap_cache_info.x++; } while (0) 46 47static struct { 48 unsigned long add_total; 49 unsigned long del_total; 50 unsigned long find_success; 51 unsigned long find_total; 52 unsigned long noent_race; 53 unsigned long exist_race; 54} swap_cache_info; 55 56void show_swap_cache_info(void) 57{ 58 printk("Swap cache: add %lu, delete %lu, find %lu/%lu, race %lu+%lu\n", 59 swap_cache_info.add_total, swap_cache_info.del_total, 60 swap_cache_info.find_success, swap_cache_info.find_total, 61 swap_cache_info.noent_race, swap_cache_info.exist_race); 62 printk("Free swap = %lukB\n", nr_swap_pages << (PAGE_SHIFT - 10)); 63 printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10)); 64} 65 66/* 67 * __add_to_swap_cache resembles add_to_page_cache on swapper_space, 68 * but sets SwapCache flag and private instead of mapping and index. 69 */ 70static int __add_to_swap_cache(struct page *page, 71 swp_entry_t entry, int gfp_mask) 72{ 73 int error; 74 75 BUG_ON(PageSwapCache(page)); 76 BUG_ON(PagePrivate(page)); 77 error = radix_tree_preload(gfp_mask); 78 if (!error) { 79 write_lock_irq(&swapper_space.tree_lock); 80 error = radix_tree_insert(&swapper_space.page_tree, 81 entry.val, page); 82 if (!error) { 83 page_cache_get(page); 84 SetPageLocked(page); 85 SetPageSwapCache(page); 86 page->private = entry.val; 87 total_swapcache_pages++; 88 pagecache_acct(1); 89 } 90 write_unlock_irq(&swapper_space.tree_lock); 91 radix_tree_preload_end(); 92 } 93 return error; 94} 95 96static int add_to_swap_cache(struct page *page, swp_entry_t entry) 97{ 98 int error; 99 100 if (!swap_duplicate(entry)) { 101 INC_CACHE_INFO(noent_race); 102 return -ENOENT; 103 } 104 error = __add_to_swap_cache(page, entry, GFP_KERNEL); 105 /* 106 * Anon pages are already on the LRU, we don't run lru_cache_add here. 107 */ 108 if (error) { 109 swap_free(entry); 110 if (error == -EEXIST) 111 INC_CACHE_INFO(exist_race); 112 return error; 113 } 114 INC_CACHE_INFO(add_total); 115 return 0; 116} 117 118/* 119 * This must be called only on pages that have 120 * been verified to be in the swap cache. 121 */ 122void __delete_from_swap_cache(struct page *page) 123{ 124 BUG_ON(!PageLocked(page)); 125 BUG_ON(!PageSwapCache(page)); 126 BUG_ON(PageWriteback(page)); 127 128 radix_tree_delete(&swapper_space.page_tree, page->private); 129 page->private = 0; 130 ClearPageSwapCache(page); 131 total_swapcache_pages--; 132 pagecache_acct(-1); 133 INC_CACHE_INFO(del_total); 134} 135 136/** 137 * add_to_swap - allocate swap space for a page 138 * @page: page we want to move to swap 139 * 140 * Allocate swap space for the page and add the page to the 141 * swap cache. Caller needs to hold the page lock. 142 */ 143int add_to_swap(struct page * page) 144{ 145 swp_entry_t entry; 146 int err; 147 148 if (!PageLocked(page)) 149 BUG(); 150 151 for (;;) { 152 entry = get_swap_page(); 153 if (!entry.val) 154 return 0; 155 156 /* 157 * Radix-tree node allocations from PF_MEMALLOC contexts could 158 * completely exhaust the page allocator. __GFP_NOMEMALLOC 159 * stops emergency reserves from being allocated. 160 * 161 * TODO: this could cause a theoretical memory reclaim 162 * deadlock in the swap out path. 163 */ 164 /* 165 * Add it to the swap cache and mark it dirty 166 */ 167 err = __add_to_swap_cache(page, entry, 168 GFP_ATOMIC|__GFP_NOMEMALLOC|__GFP_NOWARN); 169 170 switch (err) { 171 case 0: /* Success */ 172 SetPageUptodate(page); 173 SetPageDirty(page); 174 INC_CACHE_INFO(add_total); 175 return 1; 176 case -EEXIST: 177 /* Raced with "speculative" read_swap_cache_async */ 178 INC_CACHE_INFO(exist_race); 179 swap_free(entry); 180 continue; 181 default: 182 /* -ENOMEM radix-tree allocation failure */ 183 swap_free(entry); 184 return 0; 185 } 186 } 187} 188 189/* 190 * This must be called only on pages that have 191 * been verified to be in the swap cache and locked. 192 * It will never put the page into the free list, 193 * the caller has a reference on the page. 194 */ 195void delete_from_swap_cache(struct page *page) 196{ 197 swp_entry_t entry; 198 199 BUG_ON(!PageSwapCache(page)); 200 BUG_ON(!PageLocked(page)); 201 BUG_ON(PageWriteback(page)); 202 BUG_ON(PagePrivate(page)); 203 204 entry.val = page->private; 205 206 write_lock_irq(&swapper_space.tree_lock); 207 __delete_from_swap_cache(page); 208 write_unlock_irq(&swapper_space.tree_lock); 209 210 swap_free(entry); 211 page_cache_release(page); 212} 213 214/* 215 * Strange swizzling function only for use by shmem_writepage 216 */ 217int move_to_swap_cache(struct page *page, swp_entry_t entry) 218{ 219 int err = __add_to_swap_cache(page, entry, GFP_ATOMIC); 220 if (!err) { 221 remove_from_page_cache(page); 222 page_cache_release(page); /* pagecache ref */ 223 if (!swap_duplicate(entry)) 224 BUG(); 225 SetPageDirty(page); 226 INC_CACHE_INFO(add_total); 227 } else if (err == -EEXIST) 228 INC_CACHE_INFO(exist_race); 229 return err; 230} 231 232/* 233 * Strange swizzling function for shmem_getpage (and shmem_unuse) 234 */ 235int move_from_swap_cache(struct page *page, unsigned long index, 236 struct address_space *mapping) 237{ 238 int err = add_to_page_cache(page, mapping, index, GFP_ATOMIC); 239 if (!err) { 240 delete_from_swap_cache(page); 241 /* shift page from clean_pages to dirty_pages list */ 242 ClearPageDirty(page); 243 set_page_dirty(page); 244 } 245 return err; 246} 247 248/* 249 * If we are the only user, then try to free up the swap cache. 250 * 251 * Its ok to check for PageSwapCache without the page lock 252 * here because we are going to recheck again inside 253 * exclusive_swap_page() _with_ the lock. 254 * - Marcelo 255 */ 256static inline void free_swap_cache(struct page *page) 257{ 258 if (PageSwapCache(page) && !TestSetPageLocked(page)) { 259 remove_exclusive_swap_page(page); 260 unlock_page(page); 261 } 262} 263 264/* 265 * Perform a free_page(), also freeing any swap cache associated with 266 * this page if it is the last user of the page. Can not do a lock_page, 267 * as we are holding the page_table_lock spinlock. 268 */ 269void free_page_and_swap_cache(struct page *page) 270{ 271 free_swap_cache(page); 272 page_cache_release(page); 273} 274 275/* 276 * Passed an array of pages, drop them all from swapcache and then release 277 * them. They are removed from the LRU and freed if this is their last use. 278 */ 279void free_pages_and_swap_cache(struct page **pages, int nr) 280{ 281 int chunk = 16; 282 struct page **pagep = pages; 283 284 lru_add_drain(); 285 while (nr) { 286 int todo = min(chunk, nr); 287 int i; 288 289 for (i = 0; i < todo; i++) 290 free_swap_cache(pagep[i]); 291 release_pages(pagep, todo, 0); 292 pagep += todo; 293 nr -= todo; 294 } 295} 296 297/* 298 * Lookup a swap entry in the swap cache. A found page will be returned 299 * unlocked and with its refcount incremented - we rely on the kernel 300 * lock getting page table operations atomic even if we drop the page 301 * lock before returning. 302 */ 303struct page * lookup_swap_cache(swp_entry_t entry) 304{ 305 struct page *page; 306 307 page = find_get_page(&swapper_space, entry.val); 308 309 if (page) 310 INC_CACHE_INFO(find_success); 311 312 INC_CACHE_INFO(find_total); 313 return page; 314} 315 316/* 317 * Locate a page of swap in physical memory, reserving swap cache space 318 * and reading the disk if it is not already cached. 319 * A failure return means that either the page allocation failed or that 320 * the swap entry is no longer in use. 321 */ 322struct page *read_swap_cache_async(swp_entry_t entry, 323 struct vm_area_struct *vma, unsigned long addr) 324{ 325 struct page *found_page, *new_page = NULL; 326 int err; 327 328 do { 329 /* 330 * First check the swap cache. Since this is normally 331 * called after lookup_swap_cache() failed, re-calling 332 * that would confuse statistics. 333 */ 334 found_page = find_get_page(&swapper_space, entry.val); 335 if (found_page) 336 break; 337 338 /* 339 * Get a new page to read into from swap. 340 */ 341 if (!new_page) { 342 new_page = alloc_page_vma(GFP_HIGHUSER, vma, addr); 343 if (!new_page) 344 break; /* Out of memory */ 345 } 346 347 /* 348 * Associate the page with swap entry in the swap cache. 349 * May fail (-ENOENT) if swap entry has been freed since 350 * our caller observed it. May fail (-EEXIST) if there 351 * is already a page associated with this entry in the 352 * swap cache: added by a racing read_swap_cache_async, 353 * or by try_to_swap_out (or shmem_writepage) re-using 354 * the just freed swap entry for an existing page. 355 * May fail (-ENOMEM) if radix-tree node allocation failed. 356 */ 357 err = add_to_swap_cache(new_page, entry); 358 if (!err) { 359 /* 360 * Initiate read into locked page and return. 361 */ 362 lru_cache_add_active(new_page); 363 swap_readpage(NULL, new_page); 364 return new_page; 365 } 366 } while (err != -ENOENT && err != -ENOMEM); 367 368 if (new_page) 369 page_cache_release(new_page); 370 return found_page; 371} 372