| /* |
| * linux/mm/swap_state.c |
| * |
| * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds |
| * Swap reorganised 29.12.95, Stephen Tweedie |
| * |
| * Rewritten to use page cache, (C) 1998 Stephen Tweedie |
| */ |
| |
| #include <linux/mm.h> |
| #include <linux/kernel_stat.h> |
| #include <linux/swap.h> |
| #include <linux/swapctl.h> |
| #include <linux/init.h> |
| #include <linux/pagemap.h> |
| #include <linux/smp_lock.h> |
| |
| #include <asm/pgtable.h> |
| |
| /* |
| * We may have stale swap cache pages in memory: notice |
| * them here and get rid of the unnecessary final write. |
| */ |
| static int swap_writepage(struct page *page) |
| { |
| if (remove_exclusive_swap_page(page)) { |
| UnlockPage(page); |
| return 0; |
| } |
| rw_swap_page(WRITE, page); |
| return 0; |
| } |
| |
| static struct address_space_operations swap_aops = { |
| writepage: swap_writepage, |
| sync_page: block_sync_page, |
| }; |
| |
| struct address_space swapper_space = { |
| LIST_HEAD_INIT(swapper_space.clean_pages), |
| LIST_HEAD_INIT(swapper_space.dirty_pages), |
| LIST_HEAD_INIT(swapper_space.locked_pages), |
| 0, /* nrpages */ |
| &swap_aops, |
| }; |
| |
| #ifdef SWAP_CACHE_INFO |
| #define INC_CACHE_INFO(x) (swap_cache_info.x++) |
| |
| static struct { |
| unsigned long add_total; |
| unsigned long del_total; |
| unsigned long find_success; |
| unsigned long find_total; |
| unsigned long noent_race; |
| unsigned long exist_race; |
| } swap_cache_info; |
| |
| void show_swap_cache_info(void) |
| { |
| printk("Swap cache: add %lu, delete %lu, find %lu/%lu, race %lu+%lu\n", |
| swap_cache_info.add_total, swap_cache_info.del_total, |
| swap_cache_info.find_success, swap_cache_info.find_total, |
| swap_cache_info.noent_race, swap_cache_info.exist_race); |
| } |
| #else |
| #define INC_CACHE_INFO(x) do { } while (0) |
| #endif |
| |
| int add_to_swap_cache(struct page *page, swp_entry_t entry) |
| { |
| if (page->mapping) |
| BUG(); |
| if (!swap_duplicate(entry)) { |
| INC_CACHE_INFO(noent_race); |
| return -ENOENT; |
| } |
| if (add_to_page_cache_unique(page, &swapper_space, entry.val, |
| page_hash(&swapper_space, entry.val)) != 0) { |
| swap_free(entry); |
| INC_CACHE_INFO(exist_race); |
| return -EEXIST; |
| } |
| if (!PageLocked(page)) |
| BUG(); |
| if (!PageSwapCache(page)) |
| BUG(); |
| INC_CACHE_INFO(add_total); |
| return 0; |
| } |
| |
| /* |
| * This must be called only on pages that have |
| * been verified to be in the swap cache. |
| */ |
| void __delete_from_swap_cache(struct page *page) |
| { |
| if (!PageLocked(page)) |
| BUG(); |
| if (!PageSwapCache(page)) |
| BUG(); |
| ClearPageDirty(page); |
| __remove_inode_page(page); |
| INC_CACHE_INFO(del_total); |
| } |
| |
| /* |
| * This must be called only on pages that have |
| * been verified to be in the swap cache and locked. |
| * It will never put the page into the free list, |
| * the caller has a reference on the page. |
| */ |
| void delete_from_swap_cache(struct page *page) |
| { |
| swp_entry_t entry; |
| |
| if (!PageLocked(page)) |
| BUG(); |
| |
| if (unlikely(!block_flushpage(page, 0))) |
| BUG(); /* an anonymous page cannot have page->buffers set */ |
| |
| entry.val = page->index; |
| |
| spin_lock(&pagecache_lock); |
| __delete_from_swap_cache(page); |
| spin_unlock(&pagecache_lock); |
| |
| swap_free(entry); |
| page_cache_release(page); |
| } |
| |
| /* |
| * Perform a free_page(), also freeing any swap cache associated with |
| * this page if it is the last user of the page. Can not do a lock_page, |
| * as we are holding the page_table_lock spinlock. |
| */ |
| void free_page_and_swap_cache(struct page *page) |
| { |
| /* |
| * If we are the only user, then try to free up the swap cache. |
| * |
| * Its ok to check for PageSwapCache without the page lock |
| * here because we are going to recheck again inside |
| * exclusive_swap_page() _with_ the lock. |
| * - Marcelo |
| */ |
| if (PageSwapCache(page) && !TryLockPage(page)) { |
| remove_exclusive_swap_page(page); |
| UnlockPage(page); |
| } |
| page_cache_release(page); |
| } |
| |
| /* |
| * Lookup a swap entry in the swap cache. A found page will be returned |
| * unlocked and with its refcount incremented - we rely on the kernel |
| * lock getting page table operations atomic even if we drop the page |
| * lock before returning. |
| */ |
| struct page * lookup_swap_cache(swp_entry_t entry) |
| { |
| struct page *found; |
| |
| found = find_get_page(&swapper_space, entry.val); |
| /* |
| * Unsafe to assert PageSwapCache and mapping on page found: |
| * if SMP nothing prevents swapoff from deleting this page from |
| * the swap cache at this moment. find_lock_page would prevent |
| * that, but no need to change: we _have_ got the right page. |
| */ |
| INC_CACHE_INFO(find_total); |
| if (found) |
| INC_CACHE_INFO(find_success); |
| return found; |
| } |
| |
| /* |
| * Locate a page of swap in physical memory, reserving swap cache space |
| * and reading the disk if it is not already cached. |
| * A failure return means that either the page allocation failed or that |
| * the swap entry is no longer in use. |
| */ |
| struct page * read_swap_cache_async(swp_entry_t entry) |
| { |
| struct page *found_page, *new_page = NULL; |
| int err; |
| |
| do { |
| /* |
| * First check the swap cache. Since this is normally |
| * called after lookup_swap_cache() failed, re-calling |
| * that would confuse statistics: use find_get_page() |
| * directly. |
| */ |
| found_page = find_get_page(&swapper_space, entry.val); |
| if (found_page) |
| break; |
| |
| /* |
| * Get a new page to read into from swap. |
| */ |
| if (!new_page) { |
| new_page = alloc_page(GFP_HIGHUSER); |
| if (!new_page) |
| break; /* Out of memory */ |
| } |
| |
| /* |
| * Associate the page with swap entry in the swap cache. |
| * May fail (-ENOENT) if swap entry has been freed since |
| * our caller observed it. May fail (-EEXIST) if there |
| * is already a page associated with this entry in the |
| * swap cache: added by a racing read_swap_cache_async, |
| * or by try_to_swap_out (or shmem_writepage) re-using |
| * the just freed swap entry for an existing page. |
| */ |
| err = add_to_swap_cache(new_page, entry); |
| if (!err) { |
| /* |
| * Initiate read into locked page and return. |
| */ |
| rw_swap_page(READ, new_page); |
| return new_page; |
| } |
| } while (err != -ENOENT); |
| |
| if (new_page) |
| page_cache_release(new_page); |
| return found_page; |
| } |