FAILED: patch "[PATCH] mm/page_alloc: let the highest memory node recover from hopeless state" failed to apply to 6.18-stable tree

[Sasha Levin <sashal@kernel.org>]

The patch below does not apply to the 6.18-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x 83367658a01087375ede31ae343c99da03f72ac8
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '20261109200358-failed-6.18-83367658a010@kernel.org' --subject-prefix 'PATCH 6.18.y' 'HEAD^..'

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

From 83367658a01087375ede31ae343c99da03f72ac8 Mon Sep 17 00:00:00 2001
From: "Gregory Price (Meta)" <gourry@gourry.net>
Date: Mon, 19 Oct 2026 14:48:50 -0400
Subject: [PATCH] mm/page_alloc: let the highest memory node recover from
 hopeless state

free_frozen_page_commit() clears a hopeless node's kswapd failures once
its zone recovers above the high watermark, but only if another memory
node exists for allocations to fall back to.

The test `next_memory_node(nid) < MAX_NUMNODES` finds only memory nodes
with a higher id.  The highest-numbered memory node therefore never
recovers on this path, and its kswapd stays disabled until reclaim on that
node makes progress and balances it, or demotion is re-enabled.

In many cases, direct reclaim many never fully run against a lower node
(CXL/kmem), and that means its kswapd can end up full disabled in rare
situations.

To reproduce, fill the highest memory node with bound, non-THP anonymous
memory and no swap until kswapd gives up, then free it: /proc/zoneinfo
keeps showing node_unreclaimable 1 for that node.  A lower node recovers.

Count the memory nodes instead.  Adding first_memory_node != nid to the
existing test would also work, but a count says directly what the check
means: some other memory node exists.

Link: https://lore.kernel.org/20261019184850.3427905-1-gourry@gourry.net
Fixes: e7a5f249e6db ("mm: re-enable kswapd when memory pressure subsides or demotion is toggled")
Signed-off-by: Gregory Price (Meta) <gourry@gourry.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Zi Yan <ziy@nvidia.com>
Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Brendan Jackman <brendan.jackman@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Chanwon Park <flyinrm@gmail.com>
Cc: <stable@vger.kernel.org>
---
 mm/page_alloc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index a8cac5e01066c..31ba24411d36b 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2929,7 +2929,7 @@ static bool free_frozen_page_commit(struct zone *zone,
 		 * kswapd work again by resetting kswapd_failures.
 		 */
 		if (kswapd_test_hopeless(pgdat) &&
-		    next_memory_node(pgdat->node_id) < MAX_NUMNODES)
+		    num_node_state(N_MEMORY) > 1)
 			kswapd_clear_hopeless(pgdat, KSWAPD_CLEAR_HOPELESS_PCP);
 	}
 	return ret;
-- 
2.53.0