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 <zhengqi.arch@bytedance.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 1 insertions, 1 deletions

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,