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 10#include <linux/mm.h> 11#include <linux/kernel_stat.h> 12#include <linux/swap.h> 13#include <linux/swapctl.h> 14#include <linux/init.h> 15#include <linux/pagemap.h> 16#include <linux/smp_lock.h> 17 18#include <asm/pgtable.h> 19 20/* 21 * We may have stale swap cache pages in memory: notice 22 * them here and get rid of the unnecessary final write. 23 */ 24static int swap_writepage(struct page *page) 25{ 26 if (remove_exclusive_swap_page(page)) { 27 UnlockPage(page); 28 return 0; 29 } 30 rw_swap_page(WRITE, page); 31 return 0; 32} 33 34static struct address_space_operations swap_aops = { 35 writepage: swap_writepage, 36 sync_page: block_sync_page, 37}; 38 39struct address_space swapper_space = { 40 LIST_HEAD_INIT(swapper_space.clean_pages), 41 LIST_HEAD_INIT(swapper_space.dirty_pages), 42 LIST_HEAD_INIT(swapper_space.locked_pages), 43 0, /* nrpages */ 44 &swap_aops, 45}; 46 47#ifdef SWAP_CACHE_INFO 48#define INC_CACHE_INFO(x) (swap_cache_info.x++) 49 50static struct { 51 unsigned long add_total; 52 unsigned long del_total; 53 unsigned long find_success; 54 unsigned long find_total; 55 unsigned long noent_race; 56 unsigned long exist_race; 57} swap_cache_info; 58 59void show_swap_cache_info(void) 60{ 61 printk("Swap cache: add %lu, delete %lu, find %lu/%lu, race %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 swap_cache_info.noent_race, swap_cache_info.exist_race); 65} 66#else 67#define INC_CACHE_INFO(x) do { } while (0) 68#endif 69 70int add_to_swap_cache(struct page *page, swp_entry_t entry) 71{ 72 if (page->mapping) 73 BUG(); 74 if (!swap_duplicate(entry)) { 75 INC_CACHE_INFO(noent_race); 76 return -ENOENT; 77 } 78 if (add_to_page_cache_unique(page, &swapper_space, entry.val, 79 page_hash(&swapper_space, entry.val)) != 0) { 80 swap_free(entry); 81 INC_CACHE_INFO(exist_race); 82 return -EEXIST; 83 } 84 if (!PageLocked(page)) 85 BUG(); 86 if (!PageSwapCache(page)) 87 BUG(); 88 INC_CACHE_INFO(add_total); 89 return 0; 90} 91 92/* 93 * This must be called only on pages that have 94 * been verified to be in the swap cache. 95 */ 96void __delete_from_swap_cache(struct page *page) 97{ 98 if (!PageLocked(page)) 99 BUG(); 100 if (!PageSwapCache(page)) 101 BUG(); 102 ClearPageDirty(page); 103 __remove_inode_page(page); 104 INC_CACHE_INFO(del_total); 105} 106 107/* 108 * This must be called only on pages that have 109 * been verified to be in the swap cache and locked. 110 * It will never put the page into the free list, 111 * the caller has a reference on the page. 112 */ 113void delete_from_swap_cache(struct page *page) 114{ 115 swp_entry_t entry; 116 117 if (!PageLocked(page)) 118 BUG(); 119 120 if (unlikely(!block_flushpage(page, 0))) 121 BUG(); /* an anonymous page cannot have page->buffers set */ 122 123 entry.val = page->index; 124 125 spin_lock(&pagecache_lock); 126 __delete_from_swap_cache(page); 127 spin_unlock(&pagecache_lock); 128 129 swap_free(entry); 130 page_cache_release(page); 131} 132 133/* 134 * Perform a free_page(), also freeing any swap cache associated with 135 * this page if it is the last user of the page. Can not do a lock_page, 136 * as we are holding the page_table_lock spinlock. 137 */ 138void free_page_and_swap_cache(struct page *page) 139{ 140 /* 141 * If we are the only user, then try to free up the swap cache. 142 * 143 * Its ok to check for PageSwapCache without the page lock 144 * here because we are going to recheck again inside 145 * exclusive_swap_page() _with_ the lock. 146 * - Marcelo 147 */ 148 if (PageSwapCache(page) && !TryLockPage(page)) { 149 remove_exclusive_swap_page(page); 150 UnlockPage(page); 151 } 152 page_cache_release(page); 153} 154 155/* 156 * Lookup a swap entry in the swap cache. A found page will be returned 157 * unlocked and with its refcount incremented - we rely on the kernel 158 * lock getting page table operations atomic even if we drop the page 159 * lock before returning. 160 */ 161struct page * lookup_swap_cache(swp_entry_t entry) 162{ 163 struct page *found; 164 165 found = find_get_page(&swapper_space, entry.val); 166 /* 167 * Unsafe to assert PageSwapCache and mapping on page found: 168 * if SMP nothing prevents swapoff from deleting this page from 169 * the swap cache at this moment. find_lock_page would prevent 170 * that, but no need to change: we _have_ got the right page. 171 */ 172 INC_CACHE_INFO(find_total); 173 if (found) 174 INC_CACHE_INFO(find_success); 175 return found; 176} 177 178/* 179 * Locate a page of swap in physical memory, reserving swap cache space 180 * and reading the disk if it is not already cached. 181 * A failure return means that either the page allocation failed or that 182 * the swap entry is no longer in use. 183 */ 184struct page * read_swap_cache_async(swp_entry_t entry) 185{ 186 struct page *found_page, *new_page = NULL; 187 int err; 188 189 do { 190 /* 191 * First check the swap cache. Since this is normally 192 * called after lookup_swap_cache() failed, re-calling 193 * that would confuse statistics: use find_get_page() 194 * directly. 195 */ 196 found_page = find_get_page(&swapper_space, entry.val); 197 if (found_page) 198 break; 199 200 /* 201 * Get a new page to read into from swap. 202 */ 203 if (!new_page) { 204 new_page = alloc_page(GFP_HIGHUSER); 205 if (!new_page) 206 break; /* Out of memory */ 207 } 208 209 /* 210 * Associate the page with swap entry in the swap cache. 211 * May fail (-ENOENT) if swap entry has been freed since 212 * our caller observed it. May fail (-EEXIST) if there 213 * is already a page associated with this entry in the 214 * swap cache: added by a racing read_swap_cache_async, 215 * or by try_to_swap_out (or shmem_writepage) re-using 216 * the just freed swap entry for an existing page. 217 */ 218 err = add_to_swap_cache(new_page, entry); 219 if (!err) { 220 /* 221 * Initiate read into locked page and return. 222 */ 223 rw_swap_page(READ, new_page); 224 return new_page; 225 } 226 } while (err != -ENOENT); 227 228 if (new_page) 229 page_cache_release(new_page); 230 return found_page; 231} 232