From: Hugh Dickins Date: Mon, 5 Dec 2022 01:01:03 +0000 (-0800) Subject: mm: memcg: fix swapcached stat accounting X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=c449deb2b99ff2458214ed4a3526277bc9e40757;p=linux.git mm: memcg: fix swapcached stat accounting 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. Link: https://lkml.kernel.org/r/b8b96ee0-1e1e-85f8-df97-c82a11d7cd14@google.com Fixes: b6038942480e ("mm: memcg: add swapcache stat for memcg v2") Signed-off-by: Hugh Dickins Acked-by: Johannes Weiner Acked-by: Shakeel Butt Cc: Michal Hocko Cc: Roman Gushchin Cc: Yu Zhao Signed-off-by: Andrew Morton --- diff --git a/mm/memcontrol.c b/mm/memcontrol.c index ff65bc23be13c..ab457f0394ab6 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -5767,6 +5767,12 @@ static int mem_cgroup_move_account(struct page *page, } } +#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); diff --git a/mm/vmscan.c b/mm/vmscan.c index 2b42ac9ad7554..aba991c505f19 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1368,11 +1368,10 @@ static int __remove_mapping(struct address_space *mapping, struct folio *folio, 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 {