[SRU][N][O][PATCH 1/1] mm/mglru: only clear kswapd_failures if reclaimable

[Matthew Ruffell]

From: Wei Xu <weixugc at google.com>

BugLink: https://bugs.launchpad.net/bugs/2087886

lru_gen_shrink_node() unconditionally clears kswapd_failures, which can
prevent kswapd from sleeping and cause 100% kswapd cpu usage even when
kswapd repeatedly fails to make progress in reclaim.

Only clear kswap_failures in lru_gen_shrink_node() if reclaim makes some
progress, similar to shrink_node().

I happened to run into this problem in one of my tests recently.  It
requires a combination of several conditions: The allocator needs to
allocate a right amount of pages such that it can wake up kswapd
without itself being OOM killed; there is no memory for kswapd to
reclaim (My test disables swap and cleans page cache first); no other
process frees enough memory at the same time.

Link: https://lkml.kernel.org/r/20241014221211.832591-1-weixugc@google.com
Fixes: e4dde56cd208 ("mm: multi-gen LRU: per-node lru_gen_folio lists")
Signed-off-by: Wei Xu <weixugc at google.com>
Cc: Axel Rasmussen <axelrasmussen at google.com>
Cc: Brian Geffon <bgeffon at google.com>
Cc: Jan Alexander Steffens <heftig at archlinux.org>
Cc: Suleiman Souhlal <suleiman at google.com>
Cc: Yu Zhao <yuzhao at google.com>
Cc: <stable at vger.kernel.org>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
(cherry picked from commit b130ba4a6259f6b64d8af15e9e7ab1e912bcb7ad)
Signed-off-by: Matthew Ruffell <matthew.ruffell at canonical.com>
---
 mm/vmscan.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index bd489c1af228..23fb524f046b 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4940,8 +4940,8 @@ static void lru_gen_shrink_node(struct pglist_data *pgdat, struct scan_control *
 
 	blk_finish_plug(&plug);
 done:
-	/* kswapd should never fail */
-	pgdat->kswapd_failures = 0;
+	if (sc->nr_reclaimed > reclaimed)
+		pgdat->kswapd_failures = 0;
 }
 
 /******************************************************************************
-- 
2.45.2