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[2a03:2880:ff::face:b00c]) by smtp.gmail.com with ESMTPSA id t9-20020a170902e1c900b001927ebc40e2sm19138025pla.193.2023.01.04.14.29.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 Jan 2023 14:29:28 -0800 (PST) From: Nhat Pham To: akpm@linux-foundation.org Cc: hannes@cmpxchg.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, bfoster@redhat.com, willy@infradead.org, kernel-team@meta.com Subject: [PATCH] workingset: fix confusion around eviction vs refault container Date: Wed, 4 Jan 2023 14:29:27 -0800 Message-Id: <20230104222927.2378210-1-nphamcs@gmail.com> X-Mailer: git-send-email 2.30.2 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Johannes Weiner Refault decisions are made based on the lruvec where the page was evicted, as that determined its LRU order while it was alive. Stats and workingset aging must then occur on the lruvec of the new page, as that's the node and cgroup that experience the refault and that's the lruvec whose nonresident info ages out by a new resident page. Those lruvecs could be different when a page is shared between cgroups, or the refaulting page is allocated on a different node. There are currently two mix-ups: 1. When swap is available, the resident anon set must be considered when comparing the refault distance. The comparison is made against the right anon set, but the check for swap is not. When pages get evicted from a cgroup with swap, and refault in one without, this can incorrectly consider a hot refault as cold - and vice versa. Fix that by using the eviction cgroup for the swap check. 2. The stats and workingset age are updated against the wrong lruvec altogether: the right cgroup but the wrong NUMA node. When a page refaults on a different NUMA node, this will have confusing stats and distort the workingset age on a different lruvec - again possibly resulting in hot/cold misclassifications down the line. Fix the swap check and the refault pgdat to address both concerns. This was found during code review. It hasn't caused notable issues in production, suggesting that those refault-migrations are relatively rare in practice. Signed-off-by: Johannes Weiner Co-developed-by: Nhat Pham Signed-off-by: Nhat Pham --- mm/workingset.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/mm/workingset.c b/mm/workingset.c index ae7e984b23c6..79585d55c45d 100644 --- a/mm/workingset.c +++ b/mm/workingset.c @@ -457,6 +457,7 @@ void workingset_refault(struct folio *folio, void *shad= ow) */ nr =3D folio_nr_pages(folio); memcg =3D folio_memcg(folio); + pgdat =3D folio_pgdat(folio); lruvec =3D mem_cgroup_lruvec(memcg, pgdat); =20 mod_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + file, nr); @@ -474,7 +475,7 @@ void workingset_refault(struct folio *folio, void *shad= ow) workingset_size +=3D lruvec_page_state(eviction_lruvec, NR_INACTIVE_FILE); } - if (mem_cgroup_get_nr_swap_pages(memcg) > 0) { + if (mem_cgroup_get_nr_swap_pages(eviction_memcg) > 0) { workingset_size +=3D lruvec_page_state(eviction_lruvec, NR_ACTIVE_ANON); if (file) { --=20 2.30.2