[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <mjfsmy5naqj2oimgelvual6zpfinbugmbqy7kmbs2c2f7ll5jr@z4rl5zzdvrat>
Date: Sun, 27 Oct 2024 22:24:10 -0700
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Gregory Price <gourry@...rry.net>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, kernel-team@...a.com,
akpm@...ux-foundation.org, ying.huang@...el.com, weixugc@...gle.com,
dave.hansen@...ux.intel.com, osalvador@...e.de, shy828301@...il.com, stable@...r.kernel.org
Subject: Re: [PATCH] vmscan,migrate: fix double-decrement on node stats when
demoting pages
On Fri, Oct 25, 2024 at 10:17:24AM GMT, Gregory Price wrote:
> When numa balancing is enabled with demotion, vmscan will call
> migrate_pages when shrinking LRUs. Successful demotions will
> cause node vmstat numbers to double-decrement, leading to an
> imbalanced page count. The result is dmesg output like such:
>
> $ cat /proc/sys/vm/stat_refresh
>
> [77383.088417] vmstat_refresh: nr_isolated_anon -103212
> [77383.088417] vmstat_refresh: nr_isolated_file -899642
>
> This negative value may impact compaction and reclaim throttling.
>
> The double-decrement occurs in the migrate_pages path:
>
> caller to shrink_folio_list decrements the count
> shrink_folio_list
> demote_folio_list
> migrate_pages
> migrate_pages_batch
> migrate_folio_move
> migrate_folio_done
> mod_node_page_state(-ve) <- second decrement
>
> This path happens for SUCCESSFUL migrations, not failures. Typically
> callers to migrate_pages are required to handle putback/accounting for
> failures, but this is already handled in the shrink code.
>
> When accounting for migrations, instead do not decrement the count
> when the migration reason is MR_DEMOTION. As of v6.11, this demotion
> logic is the only source of MR_DEMOTION.
>
> Signed-off-by: Gregory Price <gourry@...rry.net>
> Fixes: 26aa2d199d6f2 ("mm/migrate: demote pages during reclaim")
> Cc: stable@...r.kernel.org
Reviewed-by: Shakeel Butt <shakeel.butt@...ux.dev>
This patch looks good for stable backports. For future I wonder if
instead of migrate_pages(), the caller providing the isolated folios,
manages the isolated stats (increments and decrements) similar to how
reclaim does it.
> ---
> mm/migrate.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 923ea80ba744..e3aac274cf16 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1099,7 +1099,7 @@ static void migrate_folio_done(struct folio *src,
> * not accounted to NR_ISOLATED_*. They can be recognized
> * as __folio_test_movable
> */
> - if (likely(!__folio_test_movable(src)))
> + if (likely(!__folio_test_movable(src)) && reason != MR_DEMOTION)
> mod_node_page_state(folio_pgdat(src), NR_ISOLATED_ANON +
> folio_is_file_lru(src), -folio_nr_pages(src));
>
> --
> 2.43.0
>
Powered by blists - more mailing lists