The patch titled
Subject: mm: vmscan: account for free pages to prevent infinite Loop in throttle_direct_reclaim()
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-vmscan-account-for-free-pages-to-prevent-infinite-loop-in-throttle_direct_reclaim.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-vmscan-account-for-free-pages-to-prevent-infinite-loop-in-throttle_direct_reclaim.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days
------------------------------------------------------
From: Seiji Nishikawa <snishika@xxxxxxxxxx>
Subject: mm: vmscan: account for free pages to prevent infinite Loop in throttle_direct_reclaim()
Date: Sun, 1 Dec 2024 01:12:34 +0900
The kernel hangs due to a task stuck in throttle_direct_reclaim(), caused
by a node being incorrectly deemed balanced despite pressure in certain
zones, such as ZONE_NORMAL. This issue arises from
zone_reclaimable_pages() returning 0 for zones without reclaimable file-
backed or anonymous pages, causing zones like ZONE_DMA32 with sufficient
free pages to be skipped.
The lack of swap or reclaimable pages results in ZONE_DMA32 being ignored
during reclaim, masking pressure in other zones. Consequently,
pgdat->kswapd_failures remains 0 in balance_pgdat(), preventing fallback
mechanisms in allow_direct_reclaim() from being triggered, leading to an
infinite loop in throttle_direct_reclaim().
This patch modifies zone_reclaimable_pages() to account for free pages
(NR_FREE_PAGES) when no other reclaimable pages exist. This ensures zones
with sufficient free pages are not skipped, enabling proper balancing and
reclaim behavior.
Link: https://lkml.kernel.org/r/20241130161236.433747-2-snishika@xxxxxxxxxx
Signed-off-by: Seiji Nishikawa <snishika@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vmscan.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
--- a/mm/vmscan.c~mm-vmscan-account-for-free-pages-to-prevent-infinite-loop-in-throttle_direct_reclaim
+++ a/mm/vmscan.c
@@ -374,7 +374,14 @@ unsigned long zone_reclaimable_pages(str
if (can_reclaim_anon_pages(NULL, zone_to_nid(zone), NULL))
nr += zone_page_state_snapshot(zone, NR_ZONE_INACTIVE_ANON) +
zone_page_state_snapshot(zone, NR_ZONE_ACTIVE_ANON);
-
+ /*
+ * If there are no reclaimable file-backed or anonymous pages,
+ * ensure zones with sufficient free pages are not skipped.
+ * This prevents zones like DMA32 from being ignored in reclaim
+ * scenarios where they can still help alleviate memory pressure.
+ */
+ if (nr == 0)
+ nr = zone_page_state_snapshot(zone, NR_FREE_PAGES);
return nr;
}
_
Patches currently in -mm which might be from snishika@xxxxxxxxxx are
mm-vmscan-ensure-kswapd-is-woken-up-if-the-wait-queue-is-active.patch
mm-vmscan-account-for-free-pages-to-prevent-infinite-loop-in-throttle_direct_reclaim.patch
