Re: [PATCH v4 5/6] mm: vmscan: Avoid split during shrink_folio_list()

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On 11.03.24 16:00, Ryan Roberts wrote:
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.

Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx>
---
  mm/vmscan.c | 9 +++++----
  1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index cf7d4cf47f1a..0ebec99e04c6 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1222,11 +1222,12 @@ 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 map
+					 * right away. Chances are some or all
+					 * of the tail pages can be freed
+					 * without IO.
  					 */
-					if (!folio_entire_mapcount(folio) &&
+					if (!list_empty(&folio->_deferred_list) &&
  					    split_folio_to_list(folio,
  								folio_list))
  						goto activate_locked;

Not sure if we might have to annotate that with data_race().

Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>

--
Cheers,

David / dhildenb





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