linux-kernel - [PATCH RESEND] mm: drop lruvec->lru_lock if contended when skipping folio

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Message-ID: <20240819184648.2175883-1-usamaarif642@gmail.com>
Date: Mon, 19 Aug 2024 19:46:48 +0100
From: Usama Arif <usamaarif642@...il.com>
To: akpm@...ux-foundation.org
Cc: yuzhao@...gle.com,
	david@...hat.com,
	leitao@...ian.org,
	huangzhaoyang@...il.com,
	bharata@....com,
	willy@...radead.org,
	vbabka@...e.cz,
	linux-kernel@...r.kernel.org,
	kernel-team@...a.com,
	Usama Arif <usamaarif642@...il.com>
Subject: [PATCH RESEND] mm: drop lruvec->lru_lock if contended when skipping folio

lruvec->lru_lock is highly contended and is held when calling
isolate_lru_folios. If the lru has a large number of CMA folios
consecutively, while the allocation type requested is not MIGRATE_MOVABLE,
isolate_lru_folios can hold the lock for a very long time while it
skips those. vmscan_lru_isolate tracepoint showed that skipped can go
above 70k in production and lockstat shows that waittime-max is x1000
higher without this patch.
This can cause lockups [1] and high memory pressure for extended periods of
time [2]. Hence release the lock if its contended when skipping a folio to
give other tasks a chance to acquire it and not stall.

[1] https://lore.kernel.org/all/CAOUHufbkhMZYz20aM_3rHZ3OcK4m2puji2FGpUpn_-DevGk3Kg@mail.gmail.com/
[2] https://lore.kernel.org/all/ZrssOrcJIDy8hacI@gmail.com/

Suggested-by: Yu Zhao <yuzhao@...gle.com>
Signed-off-by: Usama Arif <usamaarif642@...il.com>
Reported-by: Bharata B Rao <bharata@....com>
Tested-by: Bharata B Rao <bharata@....com>
---
 mm/vmscan.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 25e43bb3b574..bf8d39a1ad3e 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1695,8 +1695,14 @@ static unsigned long isolate_lru_folios(unsigned long nr_to_scan,
 		if (folio_zonenum(folio) > sc->reclaim_idx ||
 				skip_cma(folio, sc)) {
 			nr_skipped[folio_zonenum(folio)] += nr_pages;
-			move_to = &folios_skipped;
-			goto move;
+			list_move(&folio->lru, &folios_skipped);
+			if (!spin_is_contended(&lruvec->lru_lock))
+				continue;
+			if (!list_empty(dst))
+				break;
+			spin_unlock_irq(&lruvec->lru_lock);
+			cond_resched();
+			spin_lock_irq(&lruvec->lru_lock);
 		}
 
 		/*
-- 
2.43.5