From: Huang Ying <ying.huang@xxxxxxxxx>
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.
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
---
mm/vmscan.c | 17 +++++++++++++----
1 file changed, 13 insertions(+), 4 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index a5355022dc2f..f7e949ac9756 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1125,10 +1125,19 @@ static unsigned long shrink_page_list(struct list_head *page_list,
!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;
--
2.11.0
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