Messages in this thread Patch in this message |  | | Date | Sun, 4 Dec 2022 17:01:03 -0800 (PST) | From | Hugh Dickins <> | Subject | [PATCH] mm: memcg: fix swapcached stat accounting |
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I'd been worried by high "swapcached" counts in memcg OOM reports, thought we had a problem freeing swapcache, but it was just the accounting that was wrong.
Two issues:
1. When __remove_mapping() removes swapcache, __delete_from_swap_cache() relies on memcg_data for the right counts to be updated; but that had already been reset by mem_cgroup_swapout(). Swap those calls around - mem_cgroup_swapout() does not require the swapcached flag to be set.
6.1 commit ac35a4902374 ("mm: multi-gen LRU: minimal implementation") already made a similar swap for workingset_eviction(), but not for this.
2. memcg's "swapcached" count was added for memcg v2 stats, but displayed on OOM even for memcg v1: so mem_cgroup_move_account() ought to move it.
Fixes: b6038942480e ("mm: memcg: add swapcache stat for memcg v2") Signed-off-by: Hugh Dickins <hughd@google.com> ---
mm/memcontrol.c | 6 ++++++ mm/vmscan.c | 3 +-- 2 files changed, 7 insertions(+), 2 deletions(-)
--- 6.1-rc8/mm/memcontrol.c +++ linux/mm/memcontrol.c @@ -5741,6 +5741,12 @@ static int mem_cgroup_move_account(struc } } +#ifdef CONFIG_SWAP + if (folio_test_swapcache(folio)) { + __mod_lruvec_state(from_vec, NR_SWAPCACHE, -nr_pages); + __mod_lruvec_state(to_vec, NR_SWAPCACHE, nr_pages); + } +#endif if (folio_test_writeback(folio)) { __mod_lruvec_state(from_vec, NR_WRITEBACK, -nr_pages); __mod_lruvec_state(to_vec, NR_WRITEBACK, nr_pages); --- 6.1-rc8/mm/vmscan.c +++ linux/mm/vmscan.c @@ -1346,11 +1346,10 @@ static int __remove_mapping(struct addre if (folio_test_swapcache(folio)) { swp_entry_t swap = folio_swap_entry(folio); - /* get a shadow entry before mem_cgroup_swapout() clears folio_memcg() */ if (reclaimed && !mapping_exiting(mapping)) shadow = workingset_eviction(folio, target_memcg); - mem_cgroup_swapout(folio, swap); __delete_from_swap_cache(folio, swap, shadow); + mem_cgroup_swapout(folio, swap); xa_unlock_irq(&mapping->i_pages); put_swap_folio(folio, swap); } else {
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