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AJvYcCV8uRzuQyD1kTBLCAL8Do65o0EdzxASmmGLwZ069pSwkO+zI0maeDBFGMldqeAQAZCKd12w5ViwKw==@kvack.org X-Gm-Message-State: AOJu0YzEVCdeKczt8Uh896n4bK7DQ9CfgOoTwOhU0c2tASRm7HCgfZ49 SMZYreJrNRM9iuKsboVfPJQlCTgD+k+fz6Kf94u4kNyCkidKCTF1xlXQbtn5qBICFSWDf8py+T1 sJevhRGBFcJSWRmB1FnsYjPYpYXg= X-Google-Smtp-Source: AGHT+IFu0/SIJ4+nMuHnai7SSpAJVfjT6SCBj2snSYIIgS3/PpybgZuBVB3RtoBV2tmSRortugcY/M8XDJ1prS7XgRU= X-Received: by 2002:a17:906:6a1c:b0:a9a:81a3:59bf with SMTP id a640c23a62f3a-a9de5f656e6mr1057978466b.35.1730148360606; Mon, 28 Oct 2024 13:46:00 -0700 (PDT) MIME-Version: 1.0 References: <20241025141724.17927-1-gourry@gourry.net> In-Reply-To: <20241025141724.17927-1-gourry@gourry.net> From: Yang Shi Date: Mon, 28 Oct 2024 13:45:48 -0700 Message-ID: Subject: Re: [PATCH] vmscan,migrate: fix double-decrement on node stats when demoting pages To: Gregory Price Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel-team@meta.com, akpm@linux-foundation.org, ying.huang@intel.com, weixugc@google.com, dave.hansen@linux.intel.com, osalvador@suse.de, stable@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: DA1AB140014 X-Stat-Signature: ec5awfndsn9oj1ar3t6zwsopk6fnwjws X-Rspamd-Server: rspam09 X-Rspam-User: X-HE-Tag: 1730148345-465704 X-HE-Meta: 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 xSC4R5kL 7xo3Q2zoDFrJgzr7IsL44snxTt87tKtABbVAmuaWSQegRmDvwrst8S6bMjZHxnCPRp5f19ozZJeP2U66ZDC2L0bvO3JQYaV2jd7UNrtRtDctBzGDTYd0/OmwZ/br76zHzMAKVoVioPJrUTEOzdShWfq7ajCGVirxfdwhdhW+aLaAkGqrVjEpP0Fju+1+pT6ntiP5KFXJb9UkWltNa5aRRvU/e9tOF1yMi9jaLPhMjm3J+XGCDrCpprY9sFpAUmRFh4wpjKe4bM3WMLFces/CPQ9+RCw3KAXQ/MU8/+jJGF4tinMPJXW2ojyZq45he18NCZv69SYXPlgttpZHBLf14wPWR3aD24gHeSh4AQcPsPLA6JAheN8BTp7fy7YfSQh5oGhaTGYb4puOTrV0I7TBHpzh4RTGGNwU/WjcawSpwmWMLFWE= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Oct 25, 2024 at 7:17=E2=80=AFAM Gregory Price w= rote: > > When numa balancing is enabled with demotion, vmscan will call > migrate_pages when shrinking LRUs. Successful demotions will > cause node vmstat numbers to double-decrement, leading to an > imbalanced page count. 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 double-decrement occurs in the migrate_pages path: > > caller to shrink_folio_list decrements the count > shrink_folio_list > demote_folio_list > migrate_pages > migrate_pages_batch > migrate_folio_move > migrate_folio_done > mod_node_page_state(-ve) <- second 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. AFAIK, MGLRU doesn't dec/inc this counter, so it is not double-decrement for MGLRU. Maybe "imbalance update" is better? Anyway, it is just a nit. I'd suggest capturing the MGLRU case in the commit log too. > > 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. > > Signed-off-by: Gregory Price > Fixes: 26aa2d199d6f2 ("mm/migrate: demote pages during reclaim") > Cc: stable@vger.kernel.org Thanks for catching this. Reviewed-by: Yang Shi > --- > mm/migrate.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/migrate.c b/mm/migrate.c > index 923ea80ba744..e3aac274cf16 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -1099,7 +1099,7 @@ static void migrate_folio_done(struct folio *src, > * 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 !=3D MR_DEMOTION= ) > mod_node_page_state(folio_pgdat(src), NR_ISOLATED_ANON + > folio_is_file_lru(src), -folio_nr_pag= es(src)); > > -- > 2.43.0 >