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![Huang Ying](/assets/img/avatar_default.png)
This patch is to improve the performance of swap cache operations when the type of the swap device is not 0. Originally, the whole swap entry value is used as the key of the swap cache, even though there is one radix tree for each swap device. If the type of the swap device is not 0, the height of the radix tree of the swap cache will be increased unnecessary, especially on 64bit architecture. For example, for a 1GB swap device on the x86_64 architecture, the height of the radix tree of the swap cache is 11. But if the offset of the swap entry is used as the key of the swap cache, the height of the radix tree of the swap cache is 4. The increased height causes unnecessary radix tree descending and increased cache footprint. This patch reduces the height of the radix tree of the swap cache via using the offset of the swap entry instead of the whole swap entry value as the key of the swap cache. In 32 processes sequential swap out test case on a Xeon E5 v3 system with RAM disk as swap, the lock contention for the spinlock of the swap cache is reduced from 20.15% to 12.19%, when the type of the swap device is 1. Use the whole swap entry as key, perf-profile.calltrace.cycles-pp._raw_spin_lock_irq.__add_to_swap_cache.add_to_swap_cache.add_to_swap.shrink_page_list: 10.37, perf-profile.calltrace.cycles-pp._raw_spin_lock_irqsave.__remove_mapping.shrink_page_list.shrink_inactive_list.shrink_node_memcg: 9.78, Use the swap offset as key, perf-profile.calltrace.cycles-pp._raw_spin_lock_irq.__add_to_swap_cache.add_to_swap_cache.add_to_swap.shrink_page_list: 6.25, perf-profile.calltrace.cycles-pp._raw_spin_lock_irqsave.__remove_mapping.shrink_page_list.shrink_inactive_list.shrink_node_memcg: 5.94, Link: http://lkml.kernel.org/r/1473270649-27229-1-git-send-email-ying.huang@intel.com Signed-off-by: "Huang, Ying" <ying.huang@intel.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Vladimir Davydov <vdavydov.dev@gmail.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: Hugh Dickins <hughd@google.com> Cc: Mel Gorman <mgorman@techsingularity.net> Cc: Minchan Kim <minchan@kernel.org> Cc: Aaron Lu <aaron.lu@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
507 lines
13 KiB
C
507 lines
13 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/mm.h>
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#include <linux/gfp.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/backing-dev.h>
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#include <linux/blkdev.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.
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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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.set_page_dirty = swap_set_page_dirty,
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#ifdef CONFIG_MIGRATION
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.migratepage = migrate_page,
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#endif
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};
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struct address_space swapper_spaces[MAX_SWAPFILES] = {
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[0 ... MAX_SWAPFILES - 1] = {
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.page_tree = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
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.i_mmap_writable = ATOMIC_INIT(0),
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.a_ops = &swap_aops,
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/* swap cache doesn't use writeback related tags */
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.flags = 1 << AS_NO_WRITEBACK_TAGS,
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}
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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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} swap_cache_info;
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unsigned long total_swapcache_pages(void)
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{
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int i;
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unsigned long ret = 0;
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for (i = 0; i < MAX_SWAPFILES; i++)
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ret += swapper_spaces[i].nrpages;
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return ret;
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}
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static atomic_t swapin_readahead_hits = ATOMIC_INIT(4);
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void show_swap_cache_info(void)
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{
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printk("%lu pages in swap cache\n", total_swapcache_pages());
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printk("Swap cache stats: add %lu, delete %lu, find %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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printk("Free swap = %ldkB\n",
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get_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_locked 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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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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struct address_space *address_space;
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VM_BUG_ON_PAGE(!PageLocked(page), page);
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VM_BUG_ON_PAGE(PageSwapCache(page), page);
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VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
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get_page(page);
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SetPageSwapCache(page);
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set_page_private(page, entry.val);
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address_space = swap_address_space(entry);
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spin_lock_irq(&address_space->tree_lock);
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error = radix_tree_insert(&address_space->page_tree,
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swp_offset(entry), page);
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if (likely(!error)) {
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address_space->nrpages++;
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__inc_node_page_state(page, NR_FILE_PAGES);
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INC_CACHE_INFO(add_total);
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}
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spin_unlock_irq(&address_space->tree_lock);
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if (unlikely(error)) {
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/*
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* Only the context which have set SWAP_HAS_CACHE flag
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* would call add_to_swap_cache().
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* So add_to_swap_cache() doesn't returns -EEXIST.
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*/
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VM_BUG_ON(error == -EEXIST);
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set_page_private(page, 0UL);
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ClearPageSwapCache(page);
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put_page(page);
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}
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return error;
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}
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int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
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{
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int error;
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error = radix_tree_maybe_preload(gfp_mask);
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if (!error) {
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error = __add_to_swap_cache(page, entry);
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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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/*
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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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swp_entry_t entry;
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struct address_space *address_space;
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VM_BUG_ON_PAGE(!PageLocked(page), page);
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VM_BUG_ON_PAGE(!PageSwapCache(page), page);
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VM_BUG_ON_PAGE(PageWriteback(page), page);
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entry.val = page_private(page);
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address_space = swap_address_space(entry);
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radix_tree_delete(&address_space->page_tree, swp_offset(entry));
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set_page_private(page, 0);
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ClearPageSwapCache(page);
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address_space->nrpages--;
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__dec_node_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, struct list_head *list)
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{
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swp_entry_t entry;
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int err;
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VM_BUG_ON_PAGE(!PageLocked(page), page);
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VM_BUG_ON_PAGE(!PageUptodate(page), page);
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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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if (mem_cgroup_try_charge_swap(page, entry)) {
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swapcache_free(entry);
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return 0;
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}
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if (unlikely(PageTransHuge(page)))
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if (unlikely(split_huge_page_to_list(page, list))) {
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swapcache_free(entry);
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return 0;
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}
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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.
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*/
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err = add_to_swap_cache(page, entry,
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__GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);
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if (!err) {
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return 1;
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} else { /* -ENOMEM radix-tree allocation failure */
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/*
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* add_to_swap_cache() doesn't return -EEXIST, so we can safely
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* clear SWAP_HAS_CACHE flag.
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*/
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swapcache_free(entry);
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return 0;
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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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struct address_space *address_space;
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entry.val = page_private(page);
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address_space = swap_address_space(entry);
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spin_lock_irq(&address_space->tree_lock);
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__delete_from_swap_cache(page);
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spin_unlock_irq(&address_space->tree_lock);
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swapcache_free(entry);
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put_page(page);
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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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* try_to_free_swap() _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) && !page_mapped(page) && trylock_page(page)) {
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try_to_free_swap(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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if (!is_huge_zero_page(page))
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put_page(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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int i;
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lru_add_drain();
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for (i = 0; i < nr; i++)
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free_swap_cache(pagep[i]);
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release_pages(pagep, nr, false);
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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(swap_address_space(entry), swp_offset(entry));
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if (page) {
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INC_CACHE_INFO(find_success);
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if (TestClearPageReadahead(page))
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atomic_inc(&swapin_readahead_hits);
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}
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INC_CACHE_INFO(find_total);
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return page;
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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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bool *new_page_allocated)
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{
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struct page *found_page, *new_page = NULL;
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struct address_space *swapper_space = swap_address_space(entry);
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int err;
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*new_page_allocated = false;
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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, swp_offset(entry));
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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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* call radix_tree_preload() while we can wait.
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*/
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err = radix_tree_maybe_preload(gfp_mask & GFP_KERNEL);
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if (err)
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break;
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/*
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* Swap entry may have been freed since our caller observed it.
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*/
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err = swapcache_prepare(entry);
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if (err == -EEXIST) {
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radix_tree_preload_end();
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/*
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* We might race against get_swap_page() and stumble
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* across a SWAP_HAS_CACHE swap_map entry whose page
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* has not been brought into the swapcache yet, while
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* the other end is scheduled away waiting on discard
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* I/O completion at scan_swap_map().
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*
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* In order to avoid turning this transitory state
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* into a permanent loop around this -EEXIST case
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* if !CONFIG_PREEMPT and the I/O completion happens
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* to be waiting on the CPU waitqueue where we are now
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* busy looping, we just conditionally invoke the
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* scheduler here, if there are some more important
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* tasks to run.
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*/
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cond_resched();
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continue;
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}
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if (err) { /* swp entry is obsolete ? */
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radix_tree_preload_end();
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break;
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}
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/* May fail (-ENOMEM) if radix-tree node allocation failed. */
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__SetPageLocked(new_page);
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__SetPageSwapBacked(new_page);
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err = __add_to_swap_cache(new_page, entry);
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if (likely(!err)) {
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radix_tree_preload_end();
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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_anon(new_page);
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*new_page_allocated = true;
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return new_page;
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}
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radix_tree_preload_end();
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__ClearPageLocked(new_page);
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/*
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* add_to_swap_cache() doesn't return -EEXIST, so we can safely
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* clear SWAP_HAS_CACHE flag.
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*/
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swapcache_free(entry);
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} while (err != -ENOMEM);
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if (new_page)
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put_page(new_page);
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return found_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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bool page_was_allocated;
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struct page *retpage = __read_swap_cache_async(entry, gfp_mask,
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vma, addr, &page_was_allocated);
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if (page_was_allocated)
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swap_readpage(retpage);
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return retpage;
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}
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static unsigned long swapin_nr_pages(unsigned long offset)
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{
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static unsigned long prev_offset;
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unsigned int pages, max_pages, last_ra;
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static atomic_t last_readahead_pages;
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max_pages = 1 << READ_ONCE(page_cluster);
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if (max_pages <= 1)
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return 1;
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/*
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* This heuristic has been found to work well on both sequential and
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* random loads, swapping to hard disk or to SSD: please don't ask
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* what the "+ 2" means, it just happens to work well, that's all.
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*/
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pages = atomic_xchg(&swapin_readahead_hits, 0) + 2;
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if (pages == 2) {
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/*
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* We can have no readahead hits to judge by: but must not get
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* stuck here forever, so check for an adjacent offset instead
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* (and don't even bother to check whether swap type is same).
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*/
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if (offset != prev_offset + 1 && offset != prev_offset - 1)
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pages = 1;
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prev_offset = offset;
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} else {
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unsigned int roundup = 4;
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while (roundup < pages)
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roundup <<= 1;
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pages = roundup;
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}
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if (pages > max_pages)
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pages = max_pages;
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/* Don't shrink readahead too fast */
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last_ra = atomic_read(&last_readahead_pages) / 2;
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if (pages < last_ra)
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pages = last_ra;
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atomic_set(&last_readahead_pages, pages);
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return pages;
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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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* @gfp_mask: memory allocation flags
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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,
|
|
struct vm_area_struct *vma, unsigned long addr)
|
|
{
|
|
struct page *page;
|
|
unsigned long entry_offset = swp_offset(entry);
|
|
unsigned long offset = entry_offset;
|
|
unsigned long start_offset, end_offset;
|
|
unsigned long mask;
|
|
struct blk_plug plug;
|
|
|
|
mask = swapin_nr_pages(offset) - 1;
|
|
if (!mask)
|
|
goto skip;
|
|
|
|
/* Read a page_cluster sized and aligned cluster around offset. */
|
|
start_offset = offset & ~mask;
|
|
end_offset = offset | mask;
|
|
if (!start_offset) /* First page is swap header. */
|
|
start_offset++;
|
|
|
|
blk_start_plug(&plug);
|
|
for (offset = start_offset; 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)
|
|
continue;
|
|
if (offset != entry_offset)
|
|
SetPageReadahead(page);
|
|
put_page(page);
|
|
}
|
|
blk_finish_plug(&plug);
|
|
|
|
lru_add_drain(); /* Push any new pages onto the LRU now */
|
|
skip:
|
|
return read_swap_cache_async(entry, gfp_mask, vma, addr);
|
|
}
|