From 998ad18b00ebc0ef5a85be97fc020e710afc88ce Mon Sep 17 00:00:00 2001 From: Qi Zheng Date: Thu, 6 Apr 2023 00:18:53 +0800 Subject: mm: swap: fix performance regression on sparsetruncate-tiny 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. Link: https://lkml.kernel.org/r/20230405161854.6931-1-zhengqi.arch@bytedance.com Fixes: c2bc16817aa0 ("mm/swap: add folio_batch_move_lru()") Signed-off-by: Qi Zheng Reviewed-by: Matthew Wilcox (Oracle) Acked-by: Mel Gorman Cc: Lorenzo Stoakes Cc: Vlastimil Babka Signed-off-by: Andrew Morton --- 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, -- cgit