![Hugh Dickins](/assets/img/avatar_default.png)
Building in a filesystem on a loop device on a tmpfs file can hang when swapping, the loop thread caught in that infamous throttle_vm_writeout. In theory this is a long standing problem, which I've either never seen in practice, or long ago suppressed the recollection, after discounting my load and my tmpfs size as unrealistically high. But now, with the new aops, it has become easy to hang on one machine. Loop used to grab_cache_page before the old prepare_write to tmpfs, which seems to have been enough to free up some memory for any swapin needed; but the new write_begin lets tmpfs find or allocate the page (much nicer, since grab_cache_page missed tmpfs pages in swapcache). When allocating a fresh page, tmpfs respects loop's mapping_gfp_mask, which has __GFP_IO|__GFP_FS stripped off, and throttle_vm_writeout is designed to break out when __GFP_IO or GFP_FS is unset; but when tmfps swaps in, read_swap_cache_async allocates with GFP_HIGHUSER_MOVABLE regardless of the mapping_gfp_mask - hence the hang. So, pass gfp_mask down the line from shmem_getpage to shmem_swapin to swapin_readahead to read_swap_cache_async to add_to_swap_cache. Signed-off-by: Hugh Dickins <hugh@veritas.com> Acked-by: Rik van Riel <riel@redhat.com> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
418 lines
11 KiB
C
418 lines
11 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/swapops.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(!PageLocked(page));
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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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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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gfp_t gfp_mask)
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{
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int error;
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BUG_ON(PageLocked(page));
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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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SetPageLocked(page);
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error = __add_to_swap_cache(page, entry, gfp_mask & 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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ClearPageLocked(page);
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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, gfp_t gfp_mask,
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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_mask, 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, gfp_mask);
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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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/**
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* swapin_readahead - swap in pages in hope we need them soon
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* @entry: swap entry of this memory
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* @vma: user vma this address belongs to
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* @addr: target address for mempolicy
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*
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* Returns the struct page for entry and addr, after queueing swapin.
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*
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* Primitive swap readahead code. We simply read an aligned block of
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* (1 << page_cluster) entries in the swap area. This method is chosen
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* because it doesn't cost us any seek time. We also make sure to queue
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* the 'original' request together with the readahead ones...
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*
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* This has been extended to use the NUMA policies from the mm triggering
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* the readahead.
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*
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* Caller must hold down_read on the vma->vm_mm if vma is not NULL.
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*/
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struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
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struct vm_area_struct *vma, unsigned long addr)
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{
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int nr_pages;
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struct page *page;
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unsigned long offset;
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unsigned long end_offset;
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/*
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* Get starting offset for readaround, and number of pages to read.
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* Adjust starting address by readbehind (for NUMA interleave case)?
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* No, it's very unlikely that swap layout would follow vma layout,
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* more likely that neighbouring swap pages came from the same node:
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* so use the same "addr" to choose the same node for each swap read.
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*/
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nr_pages = valid_swaphandles(entry, &offset);
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for (end_offset = offset + nr_pages; offset < end_offset; offset++) {
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/* Ok, do the async read-ahead now */
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page = read_swap_cache_async(swp_entry(swp_type(entry), offset),
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gfp_mask, vma, addr);
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if (!page)
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break;
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page_cache_release(page);
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}
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lru_add_drain(); /* Push any new pages onto the LRU now */
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return read_swap_cache_async(entry, gfp_mask, vma, addr);
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}
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