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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id s14-20020a05620a254e00b006fb9bbb071fsm11147542qko.29.2022.12.04.17.01.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 04 Dec 2022 17:01:05 -0800 (PST) Date: Sun, 4 Dec 2022 17:01:03 -0800 (PST) From: Hugh Dickins X-X-Sender: hugh@ripple.attlocal.net To: Andrew Morton cc: Shakeel Butt , Michal Hocko , Roman Gushchin , Johannes Weiner , Yu Zhao , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH] mm: memcg: fix swapcached stat accounting Message-ID: MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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 Acked-by: Johannes Weiner Acked-by: Shakeel Butt --- 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 } } =20 +#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 =3D folio_swap_entry(folio); =20 - /* get a shadow entry before mem_cgroup_swapout() clears folio_memcg() */ if (reclaimed && !mapping_exiting(mapping)) shadow =3D 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 {