| From: Gregory Price <gourry@gourry.net> |
| Subject: vmscan,migrate: fix page count imbalance on node stats when demoting pages |
| Date: Fri, 25 Oct 2024 10:17:24 -0400 |
| |
| When numa balancing is enabled with demotion, vmscan will call |
| migrate_pages when shrinking LRUs. migrate_pages will decrement the |
| the node's isolated page count, leading to an imbalanced count when |
| invoked from (MG)LRU code. |
| |
| 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 following path produces the decrement: |
| |
| shrink_folio_list |
| demote_folio_list |
| migrate_pages |
| migrate_pages_batch |
| migrate_folio_move |
| migrate_folio_done |
| mod_node_page_state(-ve) <- 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. |
| |
| Link: https://lkml.kernel.org/r/20241025141724.17927-1-gourry@gourry.net |
| Fixes: 26aa2d199d6f ("mm/migrate: demote pages during reclaim") |
| Signed-off-by: Gregory Price <gourry@gourry.net> |
| Reviewed-by: Yang Shi <shy828301@gmail.com> |
| Reviewed-by: Davidlohr Bueso <dave@stgolabs.net> |
| Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev> |
| Reviewed-by: "Huang, Ying" <ying.huang@intel.com> |
| Reviewed-by: Oscar Salvador <osalvador@suse.de> |
| Cc: Dave Hansen <dave.hansen@linux.intel.com> |
| Cc: Wei Xu <weixugc@google.com> |
| Cc: <stable@vger.kernel.org> |
| Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
| --- |
| |
| mm/migrate.c | 2 +- |
| 1 file changed, 1 insertion(+), 1 deletion(-) |
| |
| --- a/mm/migrate.c~vmscanmigrate-fix-double-decrement-on-node-stats-when-demoting-pages |
| +++ a/mm/migrate.c |
| @@ -1178,7 +1178,7 @@ static void migrate_folio_done(struct fo |
| * 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)); |
| |
| _ |
