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![Mel Gorman](/assets/img/avatar_default.png)
It is often known at allocation time whether a page may be migrated or not. This patch adds a flag called __GFP_MOVABLE and a new mask called GFP_HIGH_MOVABLE. Allocations using the __GFP_MOVABLE can be either migrated using the page migration mechanism or reclaimed by syncing with backing storage and discarding. An API function very similar to alloc_zeroed_user_highpage() is added for __GFP_MOVABLE allocations called alloc_zeroed_user_highpage_movable(). The flags used by alloc_zeroed_user_highpage() are not changed because it would change the semantics of an existing API. After this patch is applied there are no in-kernel users of alloc_zeroed_user_highpage() so it probably should be marked deprecated if this patch is merged. Note that this patch includes a minor cleanup to the use of __GFP_ZERO in shmem.c to keep all flag modifications to inode->mapping in the shmem_dir_alloc() helper function. This clean-up suggestion is courtesy of Hugh Dickens. Additional credit goes to Christoph Lameter and Linus Torvalds for shaping the concept. Credit to Hugh Dickens for catching issues with shmem swap vector and ramfs allocations. [akpm@linux-foundation.org: build fix] [hugh@veritas.com: __GFP_ZERO cleanup] Signed-off-by: Mel Gorman <mel@csn.ul.ie> Cc: Andy Whitcroft <apw@shadowen.org> Cc: Christoph Lameter <clameter@sgi.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
367 lines
9.3 KiB
C
367 lines
9.3 KiB
C
/*
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* linux/mm/swap_state.c
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*
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* Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
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* Swap reorganised 29.12.95, Stephen Tweedie
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*
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* Rewritten to use page cache, (C) 1998 Stephen Tweedie
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*/
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#include <linux/module.h>
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#include <linux/mm.h>
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#include <linux/kernel_stat.h>
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#include <linux/swap.h>
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#include <linux/init.h>
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#include <linux/pagemap.h>
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#include <linux/buffer_head.h>
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#include <linux/backing-dev.h>
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#include <linux/pagevec.h>
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#include <linux/migrate.h>
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#include <asm/pgtable.h>
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/*
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* swapper_space is a fiction, retained to simplify the path through
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* vmscan's shrink_page_list, to make sync_page look nicer, and to allow
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* future use of radix_tree tags in the swap cache.
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*/
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static const struct address_space_operations swap_aops = {
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.writepage = swap_writepage,
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.sync_page = block_sync_page,
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.set_page_dirty = __set_page_dirty_nobuffers,
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.migratepage = migrate_page,
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};
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static struct backing_dev_info swap_backing_dev_info = {
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.capabilities = BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK,
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.unplug_io_fn = swap_unplug_io_fn,
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};
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struct address_space swapper_space = {
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.page_tree = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
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.tree_lock = __RW_LOCK_UNLOCKED(swapper_space.tree_lock),
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.a_ops = &swap_aops,
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.i_mmap_nonlinear = LIST_HEAD_INIT(swapper_space.i_mmap_nonlinear),
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.backing_dev_info = &swap_backing_dev_info,
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};
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#define INC_CACHE_INFO(x) do { swap_cache_info.x++; } while (0)
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static struct {
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unsigned long add_total;
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unsigned long del_total;
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unsigned long find_success;
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unsigned long find_total;
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unsigned long noent_race;
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unsigned long exist_race;
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} swap_cache_info;
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void show_swap_cache_info(void)
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{
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printk("Swap cache: add %lu, delete %lu, find %lu/%lu, race %lu+%lu\n",
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swap_cache_info.add_total, swap_cache_info.del_total,
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swap_cache_info.find_success, swap_cache_info.find_total,
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swap_cache_info.noent_race, swap_cache_info.exist_race);
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printk("Free swap = %lukB\n", nr_swap_pages << (PAGE_SHIFT - 10));
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printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
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}
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/*
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* __add_to_swap_cache resembles add_to_page_cache on swapper_space,
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* but sets SwapCache flag and private instead of mapping and index.
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*/
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static int __add_to_swap_cache(struct page *page, swp_entry_t entry,
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gfp_t gfp_mask)
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{
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int error;
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BUG_ON(PageSwapCache(page));
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BUG_ON(PagePrivate(page));
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error = radix_tree_preload(gfp_mask);
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if (!error) {
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write_lock_irq(&swapper_space.tree_lock);
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error = radix_tree_insert(&swapper_space.page_tree,
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entry.val, page);
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if (!error) {
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page_cache_get(page);
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SetPageLocked(page);
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SetPageSwapCache(page);
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set_page_private(page, entry.val);
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total_swapcache_pages++;
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__inc_zone_page_state(page, NR_FILE_PAGES);
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}
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write_unlock_irq(&swapper_space.tree_lock);
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radix_tree_preload_end();
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}
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return error;
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}
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static int add_to_swap_cache(struct page *page, swp_entry_t entry)
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{
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int error;
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if (!swap_duplicate(entry)) {
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INC_CACHE_INFO(noent_race);
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return -ENOENT;
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}
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error = __add_to_swap_cache(page, entry, GFP_KERNEL);
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/*
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* Anon pages are already on the LRU, we don't run lru_cache_add here.
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*/
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if (error) {
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swap_free(entry);
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if (error == -EEXIST)
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INC_CACHE_INFO(exist_race);
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return error;
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}
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INC_CACHE_INFO(add_total);
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return 0;
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}
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/*
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* This must be called only on pages that have
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* been verified to be in the swap cache.
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*/
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void __delete_from_swap_cache(struct page *page)
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{
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BUG_ON(!PageLocked(page));
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BUG_ON(!PageSwapCache(page));
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BUG_ON(PageWriteback(page));
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BUG_ON(PagePrivate(page));
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radix_tree_delete(&swapper_space.page_tree, page_private(page));
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set_page_private(page, 0);
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ClearPageSwapCache(page);
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total_swapcache_pages--;
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__dec_zone_page_state(page, NR_FILE_PAGES);
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INC_CACHE_INFO(del_total);
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}
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/**
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* add_to_swap - allocate swap space for a page
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* @page: page we want to move to swap
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*
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* Allocate swap space for the page and add the page to the
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* swap cache. Caller needs to hold the page lock.
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*/
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int add_to_swap(struct page * page, gfp_t gfp_mask)
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{
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swp_entry_t entry;
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int err;
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BUG_ON(!PageLocked(page));
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for (;;) {
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entry = get_swap_page();
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if (!entry.val)
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return 0;
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/*
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* Radix-tree node allocations from PF_MEMALLOC contexts could
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* completely exhaust the page allocator. __GFP_NOMEMALLOC
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* stops emergency reserves from being allocated.
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*
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* TODO: this could cause a theoretical memory reclaim
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* deadlock in the swap out path.
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*/
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/*
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* Add it to the swap cache and mark it dirty
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*/
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err = __add_to_swap_cache(page, entry,
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gfp_mask|__GFP_NOMEMALLOC|__GFP_NOWARN);
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switch (err) {
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case 0: /* Success */
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SetPageUptodate(page);
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SetPageDirty(page);
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INC_CACHE_INFO(add_total);
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return 1;
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case -EEXIST:
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/* Raced with "speculative" read_swap_cache_async */
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INC_CACHE_INFO(exist_race);
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swap_free(entry);
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continue;
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default:
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/* -ENOMEM radix-tree allocation failure */
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swap_free(entry);
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return 0;
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}
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}
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}
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/*
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* This must be called only on pages that have
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* been verified to be in the swap cache and locked.
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* It will never put the page into the free list,
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* the caller has a reference on the page.
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*/
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void delete_from_swap_cache(struct page *page)
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{
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swp_entry_t entry;
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entry.val = page_private(page);
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write_lock_irq(&swapper_space.tree_lock);
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__delete_from_swap_cache(page);
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write_unlock_irq(&swapper_space.tree_lock);
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swap_free(entry);
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page_cache_release(page);
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}
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/*
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* Strange swizzling function only for use by shmem_writepage
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*/
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int move_to_swap_cache(struct page *page, swp_entry_t entry)
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{
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int err = __add_to_swap_cache(page, entry, GFP_ATOMIC);
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if (!err) {
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remove_from_page_cache(page);
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page_cache_release(page); /* pagecache ref */
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if (!swap_duplicate(entry))
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BUG();
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SetPageDirty(page);
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INC_CACHE_INFO(add_total);
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} else if (err == -EEXIST)
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INC_CACHE_INFO(exist_race);
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return err;
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}
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/*
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* Strange swizzling function for shmem_getpage (and shmem_unuse)
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*/
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int move_from_swap_cache(struct page *page, unsigned long index,
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struct address_space *mapping)
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{
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int err = add_to_page_cache(page, mapping, index, GFP_ATOMIC);
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if (!err) {
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delete_from_swap_cache(page);
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/* shift page from clean_pages to dirty_pages list */
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ClearPageDirty(page);
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set_page_dirty(page);
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}
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return err;
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}
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/*
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* If we are the only user, then try to free up the swap cache.
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*
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* Its ok to check for PageSwapCache without the page lock
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* here because we are going to recheck again inside
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* exclusive_swap_page() _with_ the lock.
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* - Marcelo
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*/
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static inline void free_swap_cache(struct page *page)
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{
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if (PageSwapCache(page) && !TestSetPageLocked(page)) {
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remove_exclusive_swap_page(page);
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unlock_page(page);
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}
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}
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/*
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* Perform a free_page(), also freeing any swap cache associated with
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* this page if it is the last user of the page.
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*/
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void free_page_and_swap_cache(struct page *page)
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{
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free_swap_cache(page);
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page_cache_release(page);
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}
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/*
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* Passed an array of pages, drop them all from swapcache and then release
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* them. They are removed from the LRU and freed if this is their last use.
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*/
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void free_pages_and_swap_cache(struct page **pages, int nr)
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{
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struct page **pagep = pages;
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lru_add_drain();
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while (nr) {
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int todo = min(nr, PAGEVEC_SIZE);
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int i;
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for (i = 0; i < todo; i++)
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free_swap_cache(pagep[i]);
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release_pages(pagep, todo, 0);
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pagep += todo;
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nr -= todo;
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}
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}
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/*
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* Lookup a swap entry in the swap cache. A found page will be returned
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* unlocked and with its refcount incremented - we rely on the kernel
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* lock getting page table operations atomic even if we drop the page
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* lock before returning.
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*/
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struct page * lookup_swap_cache(swp_entry_t entry)
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{
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struct page *page;
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page = find_get_page(&swapper_space, entry.val);
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if (page)
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INC_CACHE_INFO(find_success);
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INC_CACHE_INFO(find_total);
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return page;
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}
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/*
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* Locate a page of swap in physical memory, reserving swap cache space
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* and reading the disk if it is not already cached.
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* A failure return means that either the page allocation failed or that
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* the swap entry is no longer in use.
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*/
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struct page *read_swap_cache_async(swp_entry_t entry,
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struct vm_area_struct *vma, unsigned long addr)
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{
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struct page *found_page, *new_page = NULL;
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int err;
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do {
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/*
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* First check the swap cache. Since this is normally
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* called after lookup_swap_cache() failed, re-calling
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* that would confuse statistics.
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*/
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found_page = find_get_page(&swapper_space, entry.val);
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if (found_page)
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break;
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/*
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* Get a new page to read into from swap.
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*/
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if (!new_page) {
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new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE,
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vma, addr);
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if (!new_page)
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break; /* Out of memory */
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}
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/*
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* Associate the page with swap entry in the swap cache.
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* May fail (-ENOENT) if swap entry has been freed since
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* our caller observed it. May fail (-EEXIST) if there
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* is already a page associated with this entry in the
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* swap cache: added by a racing read_swap_cache_async,
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* or by try_to_swap_out (or shmem_writepage) re-using
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* the just freed swap entry for an existing page.
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* May fail (-ENOMEM) if radix-tree node allocation failed.
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*/
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err = add_to_swap_cache(new_page, entry);
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if (!err) {
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/*
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* Initiate read into locked page and return.
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*/
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lru_cache_add_active(new_page);
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swap_readpage(NULL, new_page);
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return new_page;
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}
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} while (err != -ENOENT && err != -ENOMEM);
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if (new_page)
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page_cache_release(new_page);
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return found_page;
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}
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