swap_state.c revision aca8bf323edd31ad462dc98c107c23a5c6022ca2
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/swapops.h> 14#include <linux/init.h> 15#include <linux/pagemap.h> 16#include <linux/buffer_head.h> 17#include <linux/backing-dev.h> 18#include <linux/pagevec.h> 19#include <linux/migrate.h> 20#include <linux/page_cgroup.h> 21 22#include <asm/pgtable.h> 23 24/* 25 * swapper_space is a fiction, retained to simplify the path through 26 * vmscan's shrink_page_list, to make sync_page look nicer, and to allow 27 * future use of radix_tree tags in the swap cache. 28 */ 29static const struct address_space_operations swap_aops = { 30 .writepage = swap_writepage, 31 .sync_page = block_sync_page, 32 .set_page_dirty = __set_page_dirty_nobuffers, 33 .migratepage = migrate_page, 34}; 35 36static struct backing_dev_info swap_backing_dev_info = { 37 .capabilities = BDI_CAP_NO_ACCT_AND_WRITEBACK | BDI_CAP_SWAP_BACKED, 38 .unplug_io_fn = swap_unplug_io_fn, 39}; 40 41struct address_space swapper_space = { 42 .page_tree = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN), 43 .tree_lock = __SPIN_LOCK_UNLOCKED(swapper_space.tree_lock), 44 .a_ops = &swap_aops, 45 .i_mmap_nonlinear = LIST_HEAD_INIT(swapper_space.i_mmap_nonlinear), 46 .backing_dev_info = &swap_backing_dev_info, 47}; 48 49#define INC_CACHE_INFO(x) do { swap_cache_info.x++; } while (0) 50 51static struct { 52 unsigned long add_total; 53 unsigned long del_total; 54 unsigned long find_success; 55 unsigned long find_total; 56} swap_cache_info; 57 58void show_swap_cache_info(void) 59{ 60 printk("%lu pages in swap cache\n", total_swapcache_pages); 61 printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n", 62 swap_cache_info.add_total, swap_cache_info.del_total, 63 swap_cache_info.find_success, swap_cache_info.find_total); 64 printk("Free swap = %ldkB\n", nr_swap_pages << (PAGE_SHIFT - 10)); 65 printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10)); 66} 67 68/* 69 * add_to_swap_cache resembles add_to_page_cache_locked on swapper_space, 70 * but sets SwapCache flag and private instead of mapping and index. 71 */ 72int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask) 73{ 74 int error; 75 76 VM_BUG_ON(!PageLocked(page)); 77 VM_BUG_ON(PageSwapCache(page)); 78 VM_BUG_ON(!PageSwapBacked(page)); 79 80 error = radix_tree_preload(gfp_mask); 81 if (!error) { 82 page_cache_get(page); 83 SetPageSwapCache(page); 84 set_page_private(page, entry.val); 85 86 spin_lock_irq(&swapper_space.tree_lock); 87 error = radix_tree_insert(&swapper_space.page_tree, 88 entry.val, page); 89 if (likely(!error)) { 90 total_swapcache_pages++; 91 __inc_zone_page_state(page, NR_FILE_PAGES); 92 INC_CACHE_INFO(add_total); 93 } 94 spin_unlock_irq(&swapper_space.tree_lock); 95 radix_tree_preload_end(); 96 97 if (unlikely(error)) { 98 set_page_private(page, 0UL); 99 ClearPageSwapCache(page); 100 page_cache_release(page); 101 } 102 } 103 return error; 104} 105 106/* 107 * This must be called only on pages that have 108 * been verified to be in the swap cache. 109 */ 110void __delete_from_swap_cache(struct page *page) 111{ 112 VM_BUG_ON(!PageLocked(page)); 113 VM_BUG_ON(!PageSwapCache(page)); 114 VM_BUG_ON(PageWriteback(page)); 115 116 radix_tree_delete(&swapper_space.page_tree, page_private(page)); 117 set_page_private(page, 0); 118 ClearPageSwapCache(page); 119 total_swapcache_pages--; 120 __dec_zone_page_state(page, NR_FILE_PAGES); 121 INC_CACHE_INFO(del_total); 122} 123 124/** 125 * add_to_swap - allocate swap space for a page 126 * @page: page we want to move to swap 127 * 128 * Allocate swap space for the page and add the page to the 129 * swap cache. Caller needs to hold the page lock. 130 */ 131int add_to_swap(struct page *page) 132{ 133 swp_entry_t entry; 134 int err; 135 136 VM_BUG_ON(!PageLocked(page)); 137 VM_BUG_ON(!PageUptodate(page)); 138 139 for (;;) { 140 entry = get_swap_page(); 141 if (!entry.val) 142 return 0; 143 144 /* 145 * Radix-tree node allocations from PF_MEMALLOC contexts could 146 * completely exhaust the page allocator. __GFP_NOMEMALLOC 147 * stops emergency reserves from being allocated. 148 * 149 * TODO: this could cause a theoretical memory reclaim 150 * deadlock in the swap out path. 151 */ 152 /* 153 * Add it to the swap cache and mark it dirty 154 */ 155 err = add_to_swap_cache(page, entry, 156 __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN); 157 158 switch (err) { 159 case 0: /* Success */ 160 SetPageDirty(page); 161 return 1; 162 case -EEXIST: 163 /* Raced with "speculative" read_swap_cache_async */ 164 swapcache_free(entry, NULL); 165 continue; 166 default: 167 /* -ENOMEM radix-tree allocation failure */ 168 swapcache_free(entry, NULL); 169 return 0; 170 } 171 } 172} 173 174/* 175 * This must be called only on pages that have 176 * been verified to be in the swap cache and locked. 177 * It will never put the page into the free list, 178 * the caller has a reference on the page. 179 */ 180void delete_from_swap_cache(struct page *page) 181{ 182 swp_entry_t entry; 183 184 entry.val = page_private(page); 185 186 spin_lock_irq(&swapper_space.tree_lock); 187 __delete_from_swap_cache(page); 188 spin_unlock_irq(&swapper_space.tree_lock); 189 190 swapcache_free(entry, page); 191 page_cache_release(page); 192} 193 194/* 195 * If we are the only user, then try to free up the swap cache. 196 * 197 * Its ok to check for PageSwapCache without the page lock 198 * here because we are going to recheck again inside 199 * try_to_free_swap() _with_ the lock. 200 * - Marcelo 201 */ 202static inline void free_swap_cache(struct page *page) 203{ 204 if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) { 205 try_to_free_swap(page); 206 unlock_page(page); 207 } 208} 209 210/* 211 * Perform a free_page(), also freeing any swap cache associated with 212 * this page if it is the last user of the page. 213 */ 214void free_page_and_swap_cache(struct page *page) 215{ 216 free_swap_cache(page); 217 page_cache_release(page); 218} 219 220/* 221 * Passed an array of pages, drop them all from swapcache and then release 222 * them. They are removed from the LRU and freed if this is their last use. 223 */ 224void free_pages_and_swap_cache(struct page **pages, int nr) 225{ 226 struct page **pagep = pages; 227 228 lru_add_drain(); 229 while (nr) { 230 int todo = min(nr, PAGEVEC_SIZE); 231 int i; 232 233 for (i = 0; i < todo; i++) 234 free_swap_cache(pagep[i]); 235 release_pages(pagep, todo, 0); 236 pagep += todo; 237 nr -= todo; 238 } 239} 240 241/* 242 * Lookup a swap entry in the swap cache. A found page will be returned 243 * unlocked and with its refcount incremented - we rely on the kernel 244 * lock getting page table operations atomic even if we drop the page 245 * lock before returning. 246 */ 247struct page * lookup_swap_cache(swp_entry_t entry) 248{ 249 struct page *page; 250 251 page = find_get_page(&swapper_space, entry.val); 252 253 if (page) 254 INC_CACHE_INFO(find_success); 255 256 INC_CACHE_INFO(find_total); 257 return page; 258} 259 260/* 261 * Locate a page of swap in physical memory, reserving swap cache space 262 * and reading the disk if it is not already cached. 263 * A failure return means that either the page allocation failed or that 264 * the swap entry is no longer in use. 265 */ 266struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask, 267 struct vm_area_struct *vma, unsigned long addr) 268{ 269 struct page *found_page, *new_page = NULL; 270 int err; 271 272 do { 273 /* 274 * First check the swap cache. Since this is normally 275 * called after lookup_swap_cache() failed, re-calling 276 * that would confuse statistics. 277 */ 278 found_page = find_get_page(&swapper_space, entry.val); 279 if (found_page) 280 break; 281 282 /* 283 * Get a new page to read into from swap. 284 */ 285 if (!new_page) { 286 new_page = alloc_page_vma(gfp_mask, vma, addr); 287 if (!new_page) 288 break; /* Out of memory */ 289 } 290 291 /* 292 * Swap entry may have been freed since our caller observed it. 293 */ 294 err = swapcache_prepare(entry); 295 if (err == -EEXIST) /* seems racy */ 296 continue; 297 if (err) /* swp entry is obsolete ? */ 298 break; 299 300 /* 301 * Associate the page with swap entry in the swap cache. 302 * May fail (-EEXIST) if there is already a page associated 303 * with this entry in the swap cache: added by a racing 304 * read_swap_cache_async, or add_to_swap or shmem_writepage 305 * re-using the just freed swap entry for an existing page. 306 * May fail (-ENOMEM) if radix-tree node allocation failed. 307 */ 308 __set_page_locked(new_page); 309 SetPageSwapBacked(new_page); 310 err = add_to_swap_cache(new_page, entry, gfp_mask & GFP_KERNEL); 311 if (likely(!err)) { 312 /* 313 * Initiate read into locked page and return. 314 */ 315 lru_cache_add_anon(new_page); 316 swap_readpage(new_page); 317 return new_page; 318 } 319 ClearPageSwapBacked(new_page); 320 __clear_page_locked(new_page); 321 swapcache_free(entry, NULL); 322 } while (err != -ENOMEM); 323 324 if (new_page) 325 page_cache_release(new_page); 326 return found_page; 327} 328 329/** 330 * swapin_readahead - swap in pages in hope we need them soon 331 * @entry: swap entry of this memory 332 * @gfp_mask: memory allocation flags 333 * @vma: user vma this address belongs to 334 * @addr: target address for mempolicy 335 * 336 * Returns the struct page for entry and addr, after queueing swapin. 337 * 338 * Primitive swap readahead code. We simply read an aligned block of 339 * (1 << page_cluster) entries in the swap area. This method is chosen 340 * because it doesn't cost us any seek time. We also make sure to queue 341 * the 'original' request together with the readahead ones... 342 * 343 * This has been extended to use the NUMA policies from the mm triggering 344 * the readahead. 345 * 346 * Caller must hold down_read on the vma->vm_mm if vma is not NULL. 347 */ 348struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask, 349 struct vm_area_struct *vma, unsigned long addr) 350{ 351 int nr_pages; 352 struct page *page; 353 unsigned long offset; 354 unsigned long end_offset; 355 356 /* 357 * Get starting offset for readaround, and number of pages to read. 358 * Adjust starting address by readbehind (for NUMA interleave case)? 359 * No, it's very unlikely that swap layout would follow vma layout, 360 * more likely that neighbouring swap pages came from the same node: 361 * so use the same "addr" to choose the same node for each swap read. 362 */ 363 nr_pages = valid_swaphandles(entry, &offset); 364 for (end_offset = offset + nr_pages; offset < end_offset; offset++) { 365 /* Ok, do the async read-ahead now */ 366 page = read_swap_cache_async(swp_entry(swp_type(entry), offset), 367 gfp_mask, vma, addr); 368 if (!page) 369 break; 370 page_cache_release(page); 371 } 372 lru_add_drain(); /* Push any new pages onto the LRU now */ 373 return read_swap_cache_async(entry, gfp_mask, vma, addr); 374} 375