[PATCH 6.12.y] mm/damon: adjust isolated pages stat for DAMOS_MIGRATE_{HOT,COLD}

[PATCH 6.12.y] mm/damon: adjust isolated pages stat for DAMOS_MIGRATE_{HOT,COLD}

[SJ Park]

Callers of migrate_pages() should adjust NR_MIGRATED_{ANON,FILE} for
isolations and putback of the folios.  That for migration succeeded folios
is done by migrate_pages(), in migrate_folio_done().  That for MR_DEMOTION
reason is an exception though.

DAMOS_MIGRATE_{HOT,COLD} call migrate_pages() but mistakenly not doing the
stat adjustment.  As a result, use of DAMOS_MIGRATE_{HOT,COLD} could
corrupt the stat.  It could confuse too_many_isolated(), make compaction
and reclaim to behave in unexpected ways.  The stat corruption can be
reproduced and confirmed using DAMON user-space tool [1] on NUMA systems,
like below.

    $ numactl --hardware
    available: 2 nodes (0-1)
    [...]
    $ sudo ./damo start --damos_action migrate_hot 1
    $ sudo cat /proc/sys/vm/stat_refresh
    $ sudo dmesg
    [...]
    [   80.215554] vmstat_refresh: nr_isolated_anon -5578
    [   80.216842] vmstat_refresh: nr_isolated_file -34400

This issue was discovered [2] by Sashiko.

Link: https://lore.kernel.org/20260728140404.94476-1-sj@kernel.org
Link: https://github.com/damonitor/damo [1]
Link: https://lore.kernel.org/20260726164356.87940-1-sj@kernel.org [2]
Fixes: b51820ebea65 ("mm/damon/paddr: introduce DAMOS_MIGRATE_COLD action for demotion")
Signed-off-by: SJ Park <sj@kernel.org>
Cc: Honggyu Kim <honggyu.kim@sk.com>
Cc: Hyeongtak Ji <hyeongtak.ji@sk.com>
Cc: <stable@vger.kernel.org> # 6.11.x
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
(cherry picked from commit 1ec0e6b6f7321feb769f50d2f094a0aa6c2eda63)
Signed-off-by: SJ Park <sj@kernel.org>
---
NOTE: This patch should be applied after the manual backport [1] of
5deb65c34e68 ("mm/damon/ops-common: putback folios on invalid migrate
nid").

[1] https://lore.kernel.org/20260818062518.91960-1-sj@kernel.org

 mm/damon/paddr.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/mm/damon/paddr.c b/mm/damon/paddr.c
index 884042856f7ea..d4a4d51750f5f 100644
--- a/mm/damon/paddr.c
+++ b/mm/damon/paddr.c
@@ -414,6 +414,8 @@ static unsigned int damon_pa_migrate_folio_list(struct list_head *folio_list,
 	while (!list_empty(folio_list)) {
 		folio = lru_to_folio(folio_list);
 		list_del(&folio->lru);
+		node_stat_sub_folio(folio, NR_ISOLATED_ANON +
+				folio_is_file_lru(folio));
 		folio_putback_lru(folio);
 	}
 
@@ -437,6 +439,8 @@ static unsigned long damon_pa_migrate_pages(struct list_head *folio_list,
 			struct folio *folio = lru_to_folio(folio_list);
 
 			list_del(&folio->lru);
+			node_stat_sub_folio(folio, NR_ISOLATED_ANON +
+					folio_is_file_lru(folio));
 			folio_putback_lru(folio);
 		}
 		return nr_migrated;
@@ -487,6 +491,8 @@ static unsigned long damon_pa_migrate(struct damon_region *r, struct damos *s)
 
 		if (!folio_isolate_lru(folio))
 			goto put_folio;
+		node_stat_add_folio(folio, NR_ISOLATED_ANON +
+				folio_is_file_lru(folio));
 		list_add(&folio->lru, &folio_list);
 put_folio:
 		addr += folio_size(folio);
-- 
2.47.3

Re: [PATCH 6.12.y] mm/damon: adjust isolated pages stat for DAMOS_MIGRATE_{HOT,COLD}

[Sasha Levin]

On Mon, Aug 17, 2026 at 11:30:39PM -0700, SJ Park wrote:
> [PATCH 6.12.y] mm/damon: adjust isolated pages stat for DAMOS_MIGRATE_{HOT,COLD}

Queued for 6.12, thanks - it went in after the ops-common backport, as
your note asked.

-- 
Thanks,
Sasha