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/gfp.h> 12 #include <linux/kernel_stat.h> 13 #include <linux/swap.h> 14 #include <linux/swapops.h> 15 #include <linux/init.h> 16 #include <linux/pagemap.h> 17 #include <linux/buffer_head.h> 18 #include <linux/backing-dev.h> 19 #include <linux/pagevec.h> 20 #include <linux/migrate.h> 21 #include <linux/page_cgroup.h> 22 23 #include <asm/pgtable.h> 24 25 /* 26 * swapper_space is a fiction, retained to simplify the path through 27 * vmscan's shrink_page_list, to make sync_page look nicer, and to allow 28 * future use of radix_tree tags in the swap cache. 29 */ 30 static const struct address_space_operations swap_aops = { 31 .writepage = swap_writepage, 32 .sync_page = block_sync_page, 33 .set_page_dirty = __set_page_dirty_nobuffers, 34 .migratepage = migrate_page, 35 }; 36 37 static struct backing_dev_info swap_backing_dev_info = { 38 .name = "swap", 39 .capabilities = BDI_CAP_NO_ACCT_AND_WRITEBACK | BDI_CAP_SWAP_BACKED, 40 .unplug_io_fn = swap_unplug_io_fn, 41 }; 42 43 struct address_space swapper_space = { 44 .page_tree = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN), 45 .tree_lock = __SPIN_LOCK_UNLOCKED(swapper_space.tree_lock), 46 .a_ops = &swap_aops, 47 .i_mmap_nonlinear = LIST_HEAD_INIT(swapper_space.i_mmap_nonlinear), 48 .backing_dev_info = &swap_backing_dev_info, 49 }; 50 51 #define INC_CACHE_INFO(x) do { swap_cache_info.x++; } while (0) 52 53 static struct { 54 unsigned long add_total; 55 unsigned long del_total; 56 unsigned long find_success; 57 unsigned long find_total; 58 } swap_cache_info; 59 60 void show_swap_cache_info(void) 61 { 62 printk("%lu pages in swap cache\n", total_swapcache_pages); 63 printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n", 64 swap_cache_info.add_total, swap_cache_info.del_total, 65 swap_cache_info.find_success, swap_cache_info.find_total); 66 printk("Free swap = %ldkB\n", nr_swap_pages << (PAGE_SHIFT - 10)); 67 printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10)); 68 } 69 70 /* 71 * __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space, 72 * but sets SwapCache flag and private instead of mapping and index. 73 */ 74 static int __add_to_swap_cache(struct page *page, swp_entry_t entry) 75 { 76 int error; 77 78 VM_BUG_ON(!PageLocked(page)); 79 VM_BUG_ON(PageSwapCache(page)); 80 VM_BUG_ON(!PageSwapBacked(page)); 81 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, entry.val, page); 88 if (likely(!error)) { 89 total_swapcache_pages++; 90 __inc_zone_page_state(page, NR_FILE_PAGES); 91 INC_CACHE_INFO(add_total); 92 } 93 spin_unlock_irq(&swapper_space.tree_lock); 94 95 if (unlikely(error)) { 96 /* 97 * Only the context which have set SWAP_HAS_CACHE flag 98 * would call add_to_swap_cache(). 99 * So add_to_swap_cache() doesn't returns -EEXIST. 100 */ 101 VM_BUG_ON(error == -EEXIST); 102 set_page_private(page, 0UL); 103 ClearPageSwapCache(page); 104 page_cache_release(page); 105 } 106 107 return error; 108 } 109 110 111 int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask) 112 { 113 int error; 114 115 error = radix_tree_preload(gfp_mask); 116 if (!error) { 117 error = __add_to_swap_cache(page, entry); 118 radix_tree_preload_end(); 119 } 120 return error; 121 } 122 123 /* 124 * This must be called only on pages that have 125 * been verified to be in the swap cache. 126 */ 127 void __delete_from_swap_cache(struct page *page) 128 { 129 VM_BUG_ON(!PageLocked(page)); 130 VM_BUG_ON(!PageSwapCache(page)); 131 VM_BUG_ON(PageWriteback(page)); 132 133 radix_tree_delete(&swapper_space.page_tree, page_private(page)); 134 set_page_private(page, 0); 135 ClearPageSwapCache(page); 136 total_swapcache_pages--; 137 __dec_zone_page_state(page, NR_FILE_PAGES); 138 INC_CACHE_INFO(del_total); 139 } 140 141 /** 142 * add_to_swap - allocate swap space for a page 143 * @page: page we want to move to swap 144 * 145 * Allocate swap space for the page and add the page to the 146 * swap cache. Caller needs to hold the page lock. 147 */ 148 int add_to_swap(struct page *page) 149 { 150 swp_entry_t entry; 151 int err; 152 153 VM_BUG_ON(!PageLocked(page)); 154 VM_BUG_ON(!PageUptodate(page)); 155 156 entry = get_swap_page(); 157 if (!entry.val) 158 return 0; 159 160 /* 161 * Radix-tree node allocations from PF_MEMALLOC contexts could 162 * completely exhaust the page allocator. __GFP_NOMEMALLOC 163 * stops emergency reserves from being allocated. 164 * 165 * TODO: this could cause a theoretical memory reclaim 166 * deadlock in the swap out path. 167 */ 168 /* 169 * Add it to the swap cache and mark it dirty 170 */ 171 err = add_to_swap_cache(page, entry, 172 __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN); 173 174 if (!err) { /* Success */ 175 SetPageDirty(page); 176 return 1; 177 } else { /* -ENOMEM radix-tree allocation failure */ 178 /* 179 * add_to_swap_cache() doesn't return -EEXIST, so we can safely 180 * clear SWAP_HAS_CACHE flag. 181 */ 182 swapcache_free(entry, NULL); 183 return 0; 184 } 185 } 186 187 /* 188 * This must be called only on pages that have 189 * been verified to be in the swap cache and locked. 190 * It will never put the page into the free list, 191 * the caller has a reference on the page. 192 */ 193 void delete_from_swap_cache(struct page *page) 194 { 195 swp_entry_t entry; 196 197 entry.val = page_private(page); 198 199 spin_lock_irq(&swapper_space.tree_lock); 200 __delete_from_swap_cache(page); 201 spin_unlock_irq(&swapper_space.tree_lock); 202 203 swapcache_free(entry, page); 204 page_cache_release(page); 205 } 206 207 /* 208 * If we are the only user, then try to free up the swap cache. 209 * 210 * Its ok to check for PageSwapCache without the page lock 211 * here because we are going to recheck again inside 212 * try_to_free_swap() _with_ the lock. 213 * - Marcelo 214 */ 215 static inline void free_swap_cache(struct page *page) 216 { 217 if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) { 218 try_to_free_swap(page); 219 unlock_page(page); 220 } 221 } 222 223 /* 224 * Perform a free_page(), also freeing any swap cache associated with 225 * this page if it is the last user of the page. 226 */ 227 void free_page_and_swap_cache(struct page *page) 228 { 229 free_swap_cache(page); 230 page_cache_release(page); 231 } 232 233 /* 234 * Passed an array of pages, drop them all from swapcache and then release 235 * them. They are removed from the LRU and freed if this is their last use. 236 */ 237 void free_pages_and_swap_cache(struct page **pages, int nr) 238 { 239 struct page **pagep = pages; 240 241 lru_add_drain(); 242 while (nr) { 243 int todo = min(nr, PAGEVEC_SIZE); 244 int i; 245 246 for (i = 0; i < todo; i++) 247 free_swap_cache(pagep[i]); 248 release_pages(pagep, todo, 0); 249 pagep += todo; 250 nr -= todo; 251 } 252 } 253 254 /* 255 * Lookup a swap entry in the swap cache. A found page will be returned 256 * unlocked and with its refcount incremented - we rely on the kernel 257 * lock getting page table operations atomic even if we drop the page 258 * lock before returning. 259 */ 260 struct page * lookup_swap_cache(swp_entry_t entry) 261 { 262 struct page *page; 263 264 page = find_get_page(&swapper_space, entry.val); 265 266 if (page) 267 INC_CACHE_INFO(find_success); 268 269 INC_CACHE_INFO(find_total); 270 return page; 271 } 272 273 /* 274 * Locate a page of swap in physical memory, reserving swap cache space 275 * and reading the disk if it is not already cached. 276 * A failure return means that either the page allocation failed or that 277 * the swap entry is no longer in use. 278 */ 279 struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask, 280 struct vm_area_struct *vma, unsigned long addr) 281 { 282 struct page *found_page, *new_page = NULL; 283 int err; 284 285 do { 286 /* 287 * First check the swap cache. Since this is normally 288 * called after lookup_swap_cache() failed, re-calling 289 * that would confuse statistics. 290 */ 291 found_page = find_get_page(&swapper_space, entry.val); 292 if (found_page) 293 break; 294 295 /* 296 * Get a new page to read into from swap. 297 */ 298 if (!new_page) { 299 new_page = alloc_page_vma(gfp_mask, vma, addr); 300 if (!new_page) 301 break; /* Out of memory */ 302 } 303 304 /* 305 * call radix_tree_preload() while we can wait. 306 */ 307 err = radix_tree_preload(gfp_mask & GFP_KERNEL); 308 if (err) 309 break; 310 311 /* 312 * Swap entry may have been freed since our caller observed it. 313 */ 314 err = swapcache_prepare(entry); 315 if (err == -EEXIST) { /* seems racy */ 316 radix_tree_preload_end(); 317 continue; 318 } 319 if (err) { /* swp entry is obsolete ? */ 320 radix_tree_preload_end(); 321 break; 322 } 323 324 /* May fail (-ENOMEM) if radix-tree node allocation failed. */ 325 __set_page_locked(new_page); 326 SetPageSwapBacked(new_page); 327 err = __add_to_swap_cache(new_page, entry); 328 if (likely(!err)) { 329 radix_tree_preload_end(); 330 /* 331 * Initiate read into locked page and return. 332 */ 333 lru_cache_add_anon(new_page); 334 swap_readpage(new_page); 335 return new_page; 336 } 337 radix_tree_preload_end(); 338 ClearPageSwapBacked(new_page); 339 __clear_page_locked(new_page); 340 /* 341 * add_to_swap_cache() doesn't return -EEXIST, so we can safely 342 * clear SWAP_HAS_CACHE flag. 343 */ 344 swapcache_free(entry, NULL); 345 } while (err != -ENOMEM); 346 347 if (new_page) 348 page_cache_release(new_page); 349 return found_page; 350 } 351 352 /** 353 * swapin_readahead - swap in pages in hope we need them soon 354 * @entry: swap entry of this memory 355 * @gfp_mask: memory allocation flags 356 * @vma: user vma this address belongs to 357 * @addr: target address for mempolicy 358 * 359 * Returns the struct page for entry and addr, after queueing swapin. 360 * 361 * Primitive swap readahead code. We simply read an aligned block of 362 * (1 << page_cluster) entries in the swap area. This method is chosen 363 * because it doesn't cost us any seek time. We also make sure to queue 364 * the 'original' request together with the readahead ones... 365 * 366 * This has been extended to use the NUMA policies from the mm triggering 367 * the readahead. 368 * 369 * Caller must hold down_read on the vma->vm_mm if vma is not NULL. 370 */ 371 struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask, 372 struct vm_area_struct *vma, unsigned long addr) 373 { 374 int nr_pages; 375 struct page *page; 376 unsigned long offset; 377 unsigned long end_offset; 378 379 /* 380 * Get starting offset for readaround, and number of pages to read. 381 * Adjust starting address by readbehind (for NUMA interleave case)? 382 * No, it's very unlikely that swap layout would follow vma layout, 383 * more likely that neighbouring swap pages came from the same node: 384 * so use the same "addr" to choose the same node for each swap read. 385 */ 386 nr_pages = valid_swaphandles(entry, &offset); 387 for (end_offset = offset + nr_pages; offset < end_offset; offset++) { 388 /* Ok, do the async read-ahead now */ 389 page = read_swap_cache_async(swp_entry(swp_type(entry), offset), 390 gfp_mask, vma, addr); 391 if (!page) 392 break; 393 page_cache_release(page); 394 } 395 lru_add_drain(); /* Push any new pages onto the LRU now */ 396 return read_swap_cache_async(entry, gfp_mask, vma, addr); 397 } 398