/* * 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/module.h> #include <linux/mm.h> #include <linux/kernel_stat.h> #include <linux/swap.h> #include <linux/swapops.h> #include <linux/init.h> #include <linux/pagemap.h> #include <linux/buffer_head.h> #include <linux/backing-dev.h> #include <linux/pagevec.h> #include <linux/migrate.h> #include <linux/page_cgroup.h> #include <asm/pgtable.h> /* * swapper_space is a fiction, retained to simplify the path through * vmscan's shrink_page_list, to make sync_page look nicer, and to allow * future use of radix_tree tags in the swap cache. */ static const struct address_space_operations swap_aops = { .writepage = swap_writepage, .sync_page = block_sync_page, .set_page_dirty = __set_page_dirty_nobuffers, .migratepage = migrate_page, }; static struct backing_dev_info swap_backing_dev_info = { .capabilities = BDI_CAP_NO_ACCT_AND_WRITEBACK | BDI_CAP_SWAP_BACKED, .unplug_io_fn = swap_unplug_io_fn, }; struct address_space swapper_space = { .page_tree = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN), .tree_lock = __SPIN_LOCK_UNLOCKED(swapper_space.tree_lock), .a_ops = &swap_aops, .i_mmap_nonlinear = LIST_HEAD_INIT(swapper_space.i_mmap_nonlinear), .backing_dev_info = &swap_backing_dev_info, }; #define INC_CACHE_INFO(x) do { swap_cache_info.x++; } while (0) static struct { unsigned long add_total; unsigned long del_total; unsigned long find_success; unsigned long find_total; } swap_cache_info; void show_swap_cache_info(void) { printk("%lu pages in swap cache\n", total_swapcache_pages); printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n", swap_cache_info.add_total, swap_cache_info.del_total, swap_cache_info.find_success, swap_cache_info.find_total); printk("Free swap = %ldkB\n", nr_swap_pages << (PAGE_SHIFT - 10)); printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10)); } /* * add_to_swap_cache resembles add_to_page_cache_locked on swapper_space, * but sets SwapCache flag and private instead of mapping and index. */ int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask) { int error; VM_BUG_ON(!PageLocked(page)); VM_BUG_ON(PageSwapCache(page)); VM_BUG_ON(!PageSwapBacked(page)); error = radix_tree_preload(gfp_mask); if (!error) { page_cache_get(page); SetPageSwapCache(page); set_page_private(page, entry.val); spin_lock_irq(&swapper_space.tree_lock); error = radix_tree_insert(&swapper_space.page_tree, entry.val, page); if (likely(!error)) { total_swapcache_pages++; __inc_zone_page_state(page, NR_FILE_PAGES); INC_CACHE_INFO(add_total); } spin_unlock_irq(&swapper_space.tree_lock); radix_tree_preload_end(); if (unlikely(error)) { set_page_private(page, 0UL); ClearPageSwapCache(page); page_cache_release(page); } } return error; } /* * 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) { VM_BUG_ON(!PageLocked(page)); VM_BUG_ON(!PageSwapCache(page)); VM_BUG_ON(PageWriteback(page)); radix_tree_delete(&swapper_space.page_tree, page_private(page)); set_page_private(page, 0); ClearPageSwapCache(page); total_swapcache_pages--; __dec_zone_page_state(page, NR_FILE_PAGES); INC_CACHE_INFO(del_total); } /** * add_to_swap - allocate swap space for a page * @page: page we want to move to swap * * Allocate swap space for the page and add the page to the * swap cache. Caller needs to hold the page lock. */ int add_to_swap(struct page *page) { swp_entry_t entry; int err; VM_BUG_ON(!PageLocked(page)); VM_BUG_ON(!PageUptodate(page)); for (;;) { entry = get_swap_page(); if (!entry.val) return 0; /* * Radix-tree node allocations from PF_MEMALLOC contexts could * completely exhaust the page allocator. __GFP_NOMEMALLOC * stops emergency reserves from being allocated. * * TODO: this could cause a theoretical memory reclaim * deadlock in the swap out path. */ /* * Add it to the swap cache and mark it dirty */ err = add_to_swap_cache(page, entry, __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN); switch (err) { case 0: /* Success */ SetPageDirty(page); return 1; case -EEXIST: /* Raced with "speculative" read_swap_cache_async */ swapcache_free(entry, NULL); continue; default: /* -ENOMEM radix-tree allocation failure */ swapcache_free(entry, NULL); return 0; } } } /* * 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; entry.val = page_private(page); spin_lock_irq(&swapper_space.tree_lock); __delete_from_swap_cache(page); spin_unlock_irq(&swapper_space.tree_lock); swapcache_free(entry, page); page_cache_release(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 * try_to_free_swap() _with_ the lock. * - Marcelo */ static inline void free_swap_cache(struct page *page) { if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) { try_to_free_swap(page); unlock_page(page); } } /* * Perform a free_page(), also freeing any swap cache associated with * this page if it is the last user of the page. */ void free_page_and_swap_cache(struct page *page) { free_swap_cache(page); page_cache_release(page); } /* * Passed an array of pages, drop them all from swapcache and then release * them. They are removed from the LRU and freed if this is their last use. */ void free_pages_and_swap_cache(struct page **pages, int nr) { struct page **pagep = pages; lru_add_drain(); while (nr) { int todo = min(nr, PAGEVEC_SIZE); int i; for (i = 0; i < todo; i++) free_swap_cache(pagep[i]); release_pages(pagep, todo, 0); pagep += todo; nr -= todo; } } /* * 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 *page; page = find_get_page(&swapper_space, entry.val); if (page) INC_CACHE_INFO(find_success); INC_CACHE_INFO(find_total); return page; } /* * 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, gfp_t gfp_mask, struct vm_area_struct *vma, unsigned long addr) { 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. */ 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_vma(gfp_mask, vma, addr); if (!new_page) break; /* Out of memory */ } /* * Swap entry may have been freed since our caller observed it. */ err = swapcache_prepare(entry); if (err == -EEXIST) /* seems racy */ continue; if (err) /* swp entry is obsolete ? */ break; /* * Associate the page with swap entry in the swap cache. * 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 add_to_swap or shmem_writepage * re-using the just freed swap entry for an existing page. * May fail (-ENOMEM) if radix-tree node allocation failed. */ __set_page_locked(new_page); SetPageSwapBacked(new_page); err = add_to_swap_cache(new_page, entry, gfp_mask & GFP_KERNEL); if (likely(!err)) { /* * Initiate read into locked page and return. */ lru_cache_add_anon(new_page); swap_readpage(new_page); return new_page; } ClearPageSwapBacked(new_page); __clear_page_locked(new_page); swapcache_free(entry, NULL); } while (err != -ENOMEM); if (new_page) page_cache_release(new_page); return found_page; } /** * swapin_readahead - swap in pages in hope we need them soon * @entry: swap entry of this memory * @gfp_mask: memory allocation flags * @vma: user vma this address belongs to * @addr: target address for mempolicy * * Returns the struct page for entry and addr, after queueing swapin. * * Primitive swap readahead code. We simply read an aligned block of * (1 << page_cluster) entries in the swap area. This method is chosen * because it doesn't cost us any seek time. We also make sure to queue * the 'original' request together with the readahead ones... * * This has been extended to use the NUMA policies from the mm triggering * the readahead. * * Caller must hold down_read on the vma->vm_mm if vma is not NULL. */ struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask, struct vm_area_struct *vma, unsigned long addr) { int nr_pages; struct page *page; unsigned long offset; unsigned long end_offset; /* * Get starting offset for readaround, and number of pages to read. * Adjust starting address by readbehind (for NUMA interleave case)? * No, it's very unlikely that swap layout would follow vma layout, * more likely that neighbouring swap pages came from the same node: * so use the same "addr" to choose the same node for each swap read. */ nr_pages = valid_swaphandles(entry, &offset); for (end_offset = offset + nr_pages; offset < end_offset; offset++) { /* Ok, do the async read-ahead now */ page = read_swap_cache_async(swp_entry(swp_type(entry), offset), gfp_mask, vma, addr); if (!page) break; page_cache_release(page); } lru_add_drain(); /* Push any new pages onto the LRU now */ return read_swap_cache_async(entry, gfp_mask, vma, addr); }