--- /dev/null
+From 6aaced5abd32e2a57cd94fd64f824514d0361da8 Mon Sep 17 00:00:00 2001
+From: Seiji Nishikawa <snishika@redhat.com>
+Date: Sun, 1 Dec 2024 01:12:34 +0900
+Subject: mm: vmscan: account for free pages to prevent infinite Loop in throttle_direct_reclaim()
+
+From: Seiji Nishikawa <snishika@redhat.com>
+
+commit 6aaced5abd32e2a57cd94fd64f824514d0361da8 upstream.
+
+The task sometimes continues looping in throttle_direct_reclaim() because
+allow_direct_reclaim(pgdat) keeps returning false.
+
+ #0 [ffff80002cb6f8d0] __switch_to at ffff8000080095ac
+ #1 [ffff80002cb6f900] __schedule at ffff800008abbd1c
+ #2 [ffff80002cb6f990] schedule at ffff800008abc50c
+ #3 [ffff80002cb6f9b0] throttle_direct_reclaim at ffff800008273550
+ #4 [ffff80002cb6fa20] try_to_free_pages at ffff800008277b68
+ #5 [ffff80002cb6fae0] __alloc_pages_nodemask at ffff8000082c4660
+ #6 [ffff80002cb6fc50] alloc_pages_vma at ffff8000082e4a98
+ #7 [ffff80002cb6fca0] do_anonymous_page at ffff80000829f5a8
+ #8 [ffff80002cb6fce0] __handle_mm_fault at ffff8000082a5974
+ #9 [ffff80002cb6fd90] handle_mm_fault at ffff8000082a5bd4
+
+At this point, the pgdat contains the following two zones:
+
+ NODE: 4 ZONE: 0 ADDR: ffff00817fffe540 NAME: "DMA32"
+ SIZE: 20480 MIN/LOW/HIGH: 11/28/45
+ VM_STAT:
+ NR_FREE_PAGES: 359
+ NR_ZONE_INACTIVE_ANON: 18813
+ NR_ZONE_ACTIVE_ANON: 0
+ NR_ZONE_INACTIVE_FILE: 50
+ NR_ZONE_ACTIVE_FILE: 0
+ NR_ZONE_UNEVICTABLE: 0
+ NR_ZONE_WRITE_PENDING: 0
+ NR_MLOCK: 0
+ NR_BOUNCE: 0
+ NR_ZSPAGES: 0
+ NR_FREE_CMA_PAGES: 0
+
+ NODE: 4 ZONE: 1 ADDR: ffff00817fffec00 NAME: "Normal"
+ SIZE: 8454144 PRESENT: 98304 MIN/LOW/HIGH: 68/166/264
+ VM_STAT:
+ NR_FREE_PAGES: 146
+ NR_ZONE_INACTIVE_ANON: 94668
+ NR_ZONE_ACTIVE_ANON: 3
+ NR_ZONE_INACTIVE_FILE: 735
+ NR_ZONE_ACTIVE_FILE: 78
+ NR_ZONE_UNEVICTABLE: 0
+ NR_ZONE_WRITE_PENDING: 0
+ NR_MLOCK: 0
+ NR_BOUNCE: 0
+ NR_ZSPAGES: 0
+ NR_FREE_CMA_PAGES: 0
+
+In allow_direct_reclaim(), while processing ZONE_DMA32, the sum of
+inactive/active file-backed pages calculated in zone_reclaimable_pages()
+based on the result of zone_page_state_snapshot() is zero.
+
+Additionally, since this system lacks swap, the calculation of inactive/
+active anonymous pages is skipped.
+
+ crash> p nr_swap_pages
+ nr_swap_pages = $1937 = {
+ counter = 0
+ }
+
+As a result, ZONE_DMA32 is deemed unreclaimable and skipped, moving on to
+the processing of the next zone, ZONE_NORMAL, despite ZONE_DMA32 having
+free pages significantly exceeding the high watermark.
+
+The problem is that the pgdat->kswapd_failures hasn't been incremented.
+
+ crash> px ((struct pglist_data *) 0xffff00817fffe540)->kswapd_failures
+ $1935 = 0x0
+
+This is because the node deemed balanced. The node balancing logic in
+balance_pgdat() evaluates all zones collectively. If one or more zones
+(e.g., ZONE_DMA32) have enough free pages to meet their watermarks, the
+entire node is deemed balanced. This causes balance_pgdat() to exit early
+before incrementing the kswapd_failures, as it considers the overall
+memory state acceptable, even though some zones (like ZONE_NORMAL) remain
+under significant pressure.
+
+
+The patch ensures that zone_reclaimable_pages() includes free pages
+(NR_FREE_PAGES) in its calculation when no other reclaimable pages are
+available (e.g., file-backed or anonymous pages). This change prevents
+zones like ZONE_DMA32, which have sufficient free pages, from being
+mistakenly deemed unreclaimable. By doing so, the patch ensures proper
+node balancing, avoids masking pressure on other zones like ZONE_NORMAL,
+and prevents infinite loops in throttle_direct_reclaim() caused by
+allow_direct_reclaim(pgdat) repeatedly returning false.
+
+
+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.
+
+[akpm@linux-foundation.org: coding-style cleanups]
+Link: https://lkml.kernel.org/r/20241130164346.436469-1-snishika@redhat.com
+Link: https://lkml.kernel.org/r/20241130161236.433747-2-snishika@redhat.com
+Fixes: 5a1c84b404a7 ("mm: remove reclaim and compaction retry approximations")
+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>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ mm/vmscan.c | 9 ++++++++-
+ 1 file changed, 8 insertions(+), 1 deletion(-)
+
+--- a/mm/vmscan.c
++++ b/mm/vmscan.c
+@@ -578,7 +578,14 @@ 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;
+ }
+
projects / thirdparty / kernel / stable-queue.git / commitdiff
