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. Signed-off-by: Seiji Nishikawa <snishika@xxxxxxxxxx> --- mm/vmscan.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 76378bc257e3..fb6b4056dcce 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -374,7 +374,14 @@ unsigned long zone_reclaimable_pages(struct zone *zone) 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; } -- 2.47.0
