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/swap_state.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 006d91d8fc53..13f83c6bb1b4 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -192,9 +192,19 @@ int add_to_swap(struct page *page, struct list_head *list)
VM_BUG_ON_PAGE(!PageLocked(page), page);
VM_BUG_ON_PAGE(!PageUptodate(page), page);
- /* cannot split, skip it */
- if (PageTransHuge(page) && !can_split_huge_page(page, NULL))
- return 0;
+ if (PageTransHuge(page)) {
+ /* cannot split, skip it */
+ if (!can_split_huge_page(page, NULL))
+ return 0;
+ /*
+ * 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, list))
+ return 0;
+ }
retry:
entry = get_swap_page(page);
--
2.11.0
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