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...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Seiji Nishikawa snishika@redhat.com 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@redhat.com Signed-off-by: Seiji Nishikawa snishika@redhat.com Cc: Mel Gorman mgorman@techsingularity.net Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

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; }

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Patches currently in -mm which might be from snishika@redhat.com 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