/* *  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){	swp_entry_t ent = {.val = page_private(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);	mem_cgroup_uncharge_swapcache(page, ent);}/** * add_to_swap - allocate swap space for a page * @page: page we want to move to swap * @gfp_mask: memory allocation flags * * 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 */			swap_free(entry);			continue;		default:			/* -ENOMEM radix-tree allocation failure */			swap_free(entry);			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);	swap_free(entry);	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.		 */		if (!swap_duplicate(entry))			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(NULL, new_page);			return new_page;		}		ClearPageSwapBacked(new_page);		__clear_page_locked(new_page);		swap_free(entry);	} 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);}