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mm, swap: fix swap readahead marking

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In the original implementation, it is possible that the existing pages
in the swap cache (not newly readahead) could be marked as the readahead
pages.  This will cause the statistics of swap readahead be wrong and
influence the swap readahead algorithm too.

This is fixed via marking a page as the readahead page only if it is
newly allocated and read from the disk.

When testing with linpack, after the fixing the swap readahead hit rate
increased from ~66% to ~86%.

Link: http://lkml.kernel.org/r/20170807054038.1843-3-ying.huang@intel.com
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Shaohua Li <shli@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>
Cc: Tim Chen <tim.c.chen@intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Huang Ying 2017-09-06 16:24:33 -07:00 committed by Linus Torvalds
parent cbc65df240
commit c4fa63092f
1 changed files with 11 additions and 7 deletions
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18
mm/swap_state.c
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@ -498,7 +498,7 @@ struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
unsigned long start_offset, end_offset;
unsigned long mask;
struct blk_plug plug;
bool do_poll = true;
bool do_poll = true, page_allocated;
mask = swapin_nr_pages(offset) - 1;
if (!mask)
@ -514,14 +514,18 @@ struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
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, false);
page = __read_swap_cache_async(
swp_entry(swp_type(entry), offset),
gfp_mask, vma, addr, &page_allocated);
if (!page)
continue;
if (offset != entry_offset &&
likely(!PageTransCompound(page))) {
SetPageReadahead(page);
count_vm_event(SWAP_RA);
if (page_allocated) {
swap_readpage(page, false);
if (offset != entry_offset &&
likely(!PageTransCompound(page))) {
SetPageReadahead(page);
count_vm_event(SWAP_RA);
}
}
put_page(page);
}