![Minchan Kim](/assets/img/avatar_default.png)
Linux doesn't have an ability to free pages lazy while other OS already have been supported that named by madvise(MADV_FREE). The gain is clear that kernel can discard freed pages rather than swapping out or OOM if memory pressure happens. Without memory pressure, freed pages would be reused by userspace without another additional overhead(ex, page fault + allocation + zeroing). Jason Evans said: : Facebook has been using MAP_UNINITIALIZED : (https://lkml.org/lkml/2012/1/18/308) in some of its applications for : several years, but there are operational costs to maintaining this : out-of-tree in our kernel and in jemalloc, and we are anxious to retire it : in favor of MADV_FREE. When we first enabled MAP_UNINITIALIZED it : increased throughput for much of our workload by ~5%, and although the : benefit has decreased using newer hardware and kernels, there is still : enough benefit that we cannot reasonably retire it without a replacement. : : Aside from Facebook operations, there are numerous broadly used : applications that would benefit from MADV_FREE. The ones that immediately : come to mind are redis, varnish, and MariaDB. I don't have much insight : into Android internals and development process, but I would hope to see : MADV_FREE support eventually end up there as well to benefit applications : linked with the integrated jemalloc. : : jemalloc will use MADV_FREE once it becomes available in the Linux kernel. : In fact, jemalloc already uses MADV_FREE or equivalent everywhere it's : available: *BSD, OS X, Windows, and Solaris -- every platform except Linux : (and AIX, but I'm not sure it even compiles on AIX). The lack of : MADV_FREE on Linux forced me down a long series of increasingly : sophisticated heuristics for madvise() volume reduction, and even so this : remains a common performance issue for people using jemalloc on Linux. : Please integrate MADV_FREE; many people will benefit substantially. How it works: When madvise syscall is called, VM clears dirty bit of ptes of the range. If memory pressure happens, VM checks dirty bit of page table and if it found still "clean", it means it's a "lazyfree pages" so VM could discard the page instead of swapping out. Once there was store operation for the page before VM peek a page to reclaim, dirty bit is set so VM can swap out the page instead of discarding. One thing we should notice is that basically, MADV_FREE relies on dirty bit in page table entry to decide whether VM allows to discard the page or not. IOW, if page table entry includes marked dirty bit, VM shouldn't discard the page. However, as a example, if swap-in by read fault happens, page table entry doesn't have dirty bit so MADV_FREE could discard the page wrongly. For avoiding the problem, MADV_FREE did more checks with PageDirty and PageSwapCache. It worked out because swapped-in page lives on swap cache and since it is evicted from the swap cache, the page has PG_dirty flag. So both page flags check effectively prevent wrong discarding by MADV_FREE. However, a problem in above logic is that swapped-in page has PG_dirty still after they are removed from swap cache so VM cannot consider the page as freeable any more even if madvise_free is called in future. Look at below example for detail. ptr = malloc(); memset(ptr); .. .. .. heavy memory pressure so all of pages are swapped out .. .. var = *ptr; -> a page swapped-in and could be removed from swapcache. Then, page table doesn't mark dirty bit and page descriptor includes PG_dirty .. .. madvise_free(ptr); -> It doesn't clear PG_dirty of the page. .. .. .. .. heavy memory pressure again. .. In this time, VM cannot discard the page because the page .. has *PG_dirty* To solve the problem, this patch clears PG_dirty if only the page is owned exclusively by current process when madvise is called because PG_dirty represents ptes's dirtiness in several processes so we could clear it only if we own it exclusively. Firstly, heavy users would be general allocators(ex, jemalloc, tcmalloc and hope glibc supports it) and jemalloc/tcmalloc already have supported the feature for other OS(ex, FreeBSD) barrios@blaptop:~/benchmark/ebizzy$ lscpu Architecture: x86_64 CPU op-mode(s): 32-bit, 64-bit Byte Order: Little Endian CPU(s): 12 On-line CPU(s) list: 0-11 Thread(s) per core: 1 Core(s) per socket: 1 Socket(s): 12 NUMA node(s): 1 Vendor ID: GenuineIntel CPU family: 6 Model: 2 Stepping: 3 CPU MHz: 3200.185 BogoMIPS: 6400.53 Virtualization: VT-x Hypervisor vendor: KVM Virtualization type: full L1d cache: 32K L1i cache: 32K L2 cache: 4096K NUMA node0 CPU(s): 0-11 ebizzy benchmark(./ebizzy -S 10 -n 512) Higher avg is better. vanilla-jemalloc MADV_free-jemalloc 1 thread records: 10 records: 10 avg: 2961.90 avg: 12069.70 std: 71.96(2.43%) std: 186.68(1.55%) max: 3070.00 max: 12385.00 min: 2796.00 min: 11746.00 2 thread records: 10 records: 10 avg: 5020.00 avg: 17827.00 std: 264.87(5.28%) std: 358.52(2.01%) max: 5244.00 max: 18760.00 min: 4251.00 min: 17382.00 4 thread records: 10 records: 10 avg: 8988.80 avg: 27930.80 std: 1175.33(13.08%) std: 3317.33(11.88%) max: 9508.00 max: 30879.00 min: 5477.00 min: 21024.00 8 thread records: 10 records: 10 avg: 13036.50 avg: 33739.40 std: 170.67(1.31%) std: 5146.22(15.25%) max: 13371.00 max: 40572.00 min: 12785.00 min: 24088.00 16 thread records: 10 records: 10 avg: 11092.40 avg: 31424.20 std: 710.60(6.41%) std: 3763.89(11.98%) max: 12446.00 max: 36635.00 min: 9949.00 min: 25669.00 32 thread records: 10 records: 10 avg: 11067.00 avg: 34495.80 std: 971.06(8.77%) std: 2721.36(7.89%) max: 12010.00 max: 38598.00 min: 9002.00 min: 30636.00 In summary, MADV_FREE is about much faster than MADV_DONTNEED. This patch (of 12): Add core MADV_FREE implementation. [akpm@linux-foundation.org: small cleanups] Signed-off-by: Minchan Kim <minchan@kernel.org> Acked-by: Michal Hocko <mhocko@suse.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Mika Penttil <mika.penttila@nextfour.com> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Rik van Riel <riel@redhat.com> Cc: Mel Gorman <mgorman@suse.de> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Jason Evans <je@fb.com> Cc: Daniel Micay <danielmicay@gmail.com> Cc: "Kirill A. Shutemov" <kirill@shutemov.name> Cc: Shaohua Li <shli@kernel.org> Cc: <yalin.wang2010@gmail.com> Cc: Andy Lutomirski <luto@amacapital.net> Cc: "James E.J. Bottomley" <jejb@parisc-linux.org> Cc: "Kirill A. Shutemov" <kirill@shutemov.name> Cc: "Shaohua Li" <shli@kernel.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Chen Gang <gang.chen.5i5j@gmail.com> Cc: Chris Zankel <chris@zankel.net> Cc: Darrick J. Wong <darrick.wong@oracle.com> Cc: David S. Miller <davem@davemloft.net> Cc: Helge Deller <deller@gmx.de> Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru> Cc: Matt Turner <mattst88@gmail.com> Cc: Max Filippov <jcmvbkbc@gmail.com> Cc: Ralf Baechle <ralf@linux-mips.org> Cc: Richard Henderson <rth@twiddle.net> Cc: Roland Dreier <roland@kernel.org> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Shaohua Li <shli@kernel.org> Cc: Will Deacon <will.deacon@arm.com> Cc: Wu Fengguang <fengguang.wu@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
501 lines
13 KiB
C
501 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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}
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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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page_cache_get(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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entry.val, page);
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if (likely(!error)) {
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address_space->nrpages++;
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__inc_zone_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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page_cache_release(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, page_private(page));
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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_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, 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 (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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page_cache_release(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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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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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), entry.val);
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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, 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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* 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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ClearPageSwapBacked(new_page);
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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.
|
|
*/
|
|
swapcache_free(entry);
|
|
} while (err != -ENOMEM);
|
|
|
|
if (new_page)
|
|
page_cache_release(new_page);
|
|
return found_page;
|
|
}
|
|
|
|
/*
|
|
* Locate a page of swap in physical memory, reserving swap cache space
|
|
* and reading the disk if it is not already cached.
|
|
* A failure return means that either the page allocation failed or that
|
|
* the swap entry is no longer in use.
|
|
*/
|
|
struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
|
|
struct vm_area_struct *vma, unsigned long addr)
|
|
{
|
|
bool page_was_allocated;
|
|
struct page *retpage = __read_swap_cache_async(entry, gfp_mask,
|
|
vma, addr, &page_was_allocated);
|
|
|
|
if (page_was_allocated)
|
|
swap_readpage(retpage);
|
|
|
|
return retpage;
|
|
}
|
|
|
|
static unsigned long swapin_nr_pages(unsigned long offset)
|
|
{
|
|
static unsigned long prev_offset;
|
|
unsigned int pages, max_pages, last_ra;
|
|
static atomic_t last_readahead_pages;
|
|
|
|
max_pages = 1 << READ_ONCE(page_cluster);
|
|
if (max_pages <= 1)
|
|
return 1;
|
|
|
|
/*
|
|
* This heuristic has been found to work well on both sequential and
|
|
* random loads, swapping to hard disk or to SSD: please don't ask
|
|
* what the "+ 2" means, it just happens to work well, that's all.
|
|
*/
|
|
pages = atomic_xchg(&swapin_readahead_hits, 0) + 2;
|
|
if (pages == 2) {
|
|
/*
|
|
* We can have no readahead hits to judge by: but must not get
|
|
* stuck here forever, so check for an adjacent offset instead
|
|
* (and don't even bother to check whether swap type is same).
|
|
*/
|
|
if (offset != prev_offset + 1 && offset != prev_offset - 1)
|
|
pages = 1;
|
|
prev_offset = offset;
|
|
} else {
|
|
unsigned int roundup = 4;
|
|
while (roundup < pages)
|
|
roundup <<= 1;
|
|
pages = roundup;
|
|
}
|
|
|
|
if (pages > max_pages)
|
|
pages = max_pages;
|
|
|
|
/* Don't shrink readahead too fast */
|
|
last_ra = atomic_read(&last_readahead_pages) / 2;
|
|
if (pages < last_ra)
|
|
pages = last_ra;
|
|
atomic_set(&last_readahead_pages, pages);
|
|
|
|
return pages;
|
|
}
|
|
|
|
/**
|
|
* swapin_readahead - swap in pages in hope we need them soon
|
|
* @entry: swap entry of this memory
|
|
* @gfp_mask: memory allocation flags
|
|
* @vma: user vma this address belongs to
|
|
* @addr: target address for mempolicy
|
|
*
|
|
* Returns the struct page for entry and addr, after queueing swapin.
|
|
*
|
|
* Primitive swap readahead code. We simply read an aligned block of
|
|
* (1 << page_cluster) entries in the swap area. This method is chosen
|
|
* because it doesn't cost us any seek time. We also make sure to queue
|
|
* the 'original' request together with the readahead ones...
|
|
*
|
|
* This has been extended to use the NUMA policies from the mm triggering
|
|
* the readahead.
|
|
*
|
|
* Caller must hold down_read on the vma->vm_mm if vma is not NULL.
|
|
*/
|
|
struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
|
|
struct vm_area_struct *vma, unsigned long addr)
|
|
{
|
|
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);
|
|
page_cache_release(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);
|
|
}
|