The ->percpu_pvec_drained was originally introduced by
commit d9ed0d08b6c6 ("mm: only drain per-cpu pagevecs once per
pagevec usage") to drain per-cpu pagevecs only once per pagevec
usage. But after converting the swap code to be more folio-based,
the commit c2bc16817aa0 ("mm/swap: add folio_batch_move_lru()")
breaks this logic, which would cause ->percpu_pvec_drained to be
reset to false, that means per-cpu pagevecs will be drained
multiple times per pagevec usage.
In theory, there should be no functional changes when converting
code to be more folio-based. We should call folio_batch_reinit()
in folio_batch_move_lru() instead of folio_batch_init(). And to
verify that we still need ->percpu_pvec_drained, I ran
mmtests/sparsetruncate-tiny and got the following data:
baseline with
baseline/ patch/
Min Time 326.00 ( 0.00%) 328.00 ( -0.61%)
1st-qrtle Time 334.00 ( 0.00%) 336.00 ( -0.60%)
2nd-qrtle Time 338.00 ( 0.00%) 341.00 ( -0.89%)
3rd-qrtle Time 343.00 ( 0.00%) 347.00 ( -1.17%)
Max-1 Time 326.00 ( 0.00%) 328.00 ( -0.61%)
Max-5 Time 327.00 ( 0.00%) 330.00 ( -0.92%)
Max-10 Time 328.00 ( 0.00%) 331.00 ( -0.91%)
Max-90 Time 350.00 ( 0.00%) 357.00 ( -2.00%)
Max-95 Time 395.00 ( 0.00%) 390.00 ( 1.27%)
Max-99 Time 508.00 ( 0.00%) 434.00 ( 14.57%)
Max Time 547.00 ( 0.00%) 476.00 ( 12.98%)
Amean Time 344.61 ( 0.00%) 345.56 * -0.28%*
Stddev Time 30.34 ( 0.00%) 19.51 ( 35.69%)
CoeffVar Time 8.81 ( 0.00%) 5.65 ( 35.87%)
BAmean-99 Time 342.38 ( 0.00%) 344.27 ( -0.55%)
BAmean-95 Time 338.58 ( 0.00%) 341.87 ( -0.97%)
BAmean-90 Time 336.89 ( 0.00%) 340.26 ( -1.00%)
BAmean-75 Time 335.18 ( 0.00%) 338.40 ( -0.96%)
BAmean-50 Time 332.54 ( 0.00%) 335.42 ( -0.87%)
BAmean-25 Time 329.30 ( 0.00%) 332.00 ( -0.82%)
>From the above it can be seen that we get similar data to when
->percpu_pvec_drained was introduced, so we still need it. Let's
call folio_batch_reinit() in folio_batch_move_lru() to restore
the original logic.
Fixes: c2bc16817aa0 ("mm/swap: add folio_batch_move_lru()")
Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
---
Changlog in v1 to v2:
- revise commit message and add test data
mm/swap.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/swap.c b/mm/swap.c
index 57cb01b042f6..423199ee8478 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -222,7 +222,7 @@ static void folio_batch_move_lru(struct folio_batch *fbatch, move_fn_t move_fn)
if (lruvec)
unlock_page_lruvec_irqrestore(lruvec, flags);
folios_put(fbatch->folios, folio_batch_count(fbatch));
- folio_batch_init(fbatch);
+ folio_batch_reinit(fbatch);
}
static void folio_batch_add_and_move(struct folio_batch *fbatch,
--
2.20.1
