Now that swap supports storing all mTHP sizes, avoid splitting large
folios before swap-out. This benefits performance of the swap-out path
by eliding split_folio_to_list(), which is expensive, and also sets us
up for swapping in large folios in a future series.
If the folio is partially mapped, we continue to split it since we want
to avoid the extra IO overhead and storage of writing out pages
uneccessarily.
THP_SWPOUT and THP_SWPOUT_FALLBACK counters should continue to count
events only for PMD-mappable folios to avoid user confusion. THP_SWPOUT
already has the appropriate guard. Add a guard for THP_SWPOUT_FALLBACK.
It may be appropriate to add per-size counters in future.
Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
Reviewed-by: Barry Song <v-songbaohua@xxxxxxxx>
Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx>
---
mm/vmscan.c | 17 +++++++++++------
1 file changed, 11 insertions(+), 6 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 00adaf1cb2c3..ffc4553c8615 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1223,11 +1223,12 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
if (!can_split_folio(folio, NULL))
goto activate_locked;
/*
- * Split folios without a PMD map right
- * away. Chances are some or all of the
- * tail pages can be freed without IO.
+ * Split partially mapped folios right
+ * away. We can free the unmapped pages
+ * without IO.
*/
- if (!folio_entire_mapcount(folio) &&
+ if (data_race(!list_empty(
+ &folio->_deferred_list)) &&
split_folio_to_list(folio,
folio_list))
goto activate_locked;
@@ -1240,8 +1241,12 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
folio_list))
goto activate_locked;
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
- count_memcg_folio_events(folio, THP_SWPOUT_FALLBACK, 1);
- count_vm_event(THP_SWPOUT_FALLBACK);
+ if (nr_pages >= HPAGE_PMD_NR) {
+ count_memcg_folio_events(folio,
+ THP_SWPOUT_FALLBACK, 1);
+ count_vm_event(
+ THP_SWPOUT_FALLBACK);
+ }
#endif
if (!add_to_swap(folio))
goto activate_locked_split;
--
2.25.1
