The patch titled
Subject: mm, THP, swap: enable THP swap optimization only if has compound map
has been added to the -mm tree. Its filename is
mm-thp-swap-enable-thp-swap-optimization-only-if-has-compound-map.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-thp-swap-enable-thp-swap-optimization-only-if-has-compound-map.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-thp-swap-enable-thp-swap-optimization-only-if-has-compound-map.patch
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------------------------------------------------------
From: Huang Ying <ying.huang@xxxxxxxxx>
Subject: mm, THP, swap: enable THP swap optimization only if has compound map
If there is no compound map for a THP (Transparent Huge Page), it is
possible that the map count of some sub-pages of the THP is 0. So it is
better to split the THP before swapping out. In this way, the sub-pages
not mapped will be freed, and we can avoid the unnecessary swap out
operations for these sub-pages.
Link: http://lkml.kernel.org/r/20170515112522.32457-6-ying.huang@xxxxxxxxx
Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Ebru Akagunduz <ebru.akagunduz@xxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Shaohua Li <shli@xxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vmscan.c | 17 +++++++++++++----
1 file changed, 13 insertions(+), 4 deletions(-)
diff -puN mm/vmscan.c~mm-thp-swap-enable-thp-swap-optimization-only-if-has-compound-map mm/vmscan.c
--- a/mm/vmscan.c~mm-thp-swap-enable-thp-swap-optimization-only-if-has-compound-map
+++ a/mm/vmscan.c
@@ -1125,10 +1125,19 @@ static unsigned long shrink_page_list(st
!PageSwapCache(page)) {
if (!(sc->gfp_mask & __GFP_IO))
goto keep_locked;
- /* cannot split THP, skip it */
- if (PageTransHuge(page) &&
- !can_split_huge_page(page, NULL))
- goto activate_locked;
+ if (PageTransHuge(page)) {
+ /* cannot split THP, skip it */
+ if (!can_split_huge_page(page, NULL))
+ goto activate_locked;
+ /*
+ * Split pages without a PMD map right
+ * away. Chances are some or all of the
+ * tail pages can be freed without IO.
+ */
+ if (!compound_mapcount(page) &&
+ split_huge_page_to_list(page, page_list))
+ goto activate_locked;
+ }
if (!add_to_swap(page)) {
if (!PageTransHuge(page))
goto activate_locked;
_
Patches currently in -mm which might be from ying.huang@xxxxxxxxx are
mm-thp-swap-delay-splitting-thp-during-swap-out.patch
mm-thp-swap-check-whether-thp-can-be-split-firstly.patch
mm-thp-swap-enable-thp-swap-optimization-only-if-has-compound-map.patch
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