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AJvYcCWQOPXGZRiPuwCeOXCfivsc+hZTxFoFiXlPFCA5G3px2i0gbJafQ3Xixc8oJkO8gF+S8+qQemJ9da6KS+8Ec/jm3j4= X-Gm-Message-State: AOJu0YwHqb3hQngBqZv0wjKlTfHr4FzHI8gpLIit8GmOZ5hJmb+frGUk BxgFZPuCYXnrhiCqK5/emiMGiWaeSE1lFS7pC/3AHk/p0em+/FbNeMiOQdYSlKor8o+M0TaEw8J BzyA08Bsqes+DLOUG4/hingFFtZ7YdV/27ZEe X-Google-Smtp-Source: AGHT+IHiRAz+VJrjTyQErBwaHiOk6l7d/y+oDGAU/XgFssJkdn8QbudNBadDoKfGqCjFhWshhxfGxx9cQBFG8uqsLm4= X-Received: by 2002:a17:906:a288:b0:a59:c728:5421 with SMTP id i8-20020a170906a28800b00a59c7285421mr3071578ejz.68.1715023389989; Mon, 06 May 2024 12:23:09 -0700 (PDT) MIME-Version: 1.0 References: <20240506170024.202111-1-yosryahmed@google.com> In-Reply-To: From: Yosry Ahmed Date: Mon, 6 May 2024 12:22:31 -0700 Message-ID: Subject: Re: [PATCH] mm: do not update memcg stats for NR_{FILE/SHMEM}_PMDMAPPED To: David Hildenbrand Cc: Andrew Morton , Shakeel Butt , Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, syzbot+9319a4268a640e26b72b@syzkaller.appspotmail.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: A05B040018 X-Stat-Signature: r66qfzip783wtgbwenkjyuh5rrs8szh1 X-Rspam-User: X-HE-Tag: 1715023391-693233 X-HE-Meta: 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 JFP0m3XK EGiDMup/S/nEseBCgGuLn0ksgWrq9KBTao3f6Oo3nxZeef7Y1GAy2pcZBr5HB7NqT4gKGZoW0kNpZi5Anzt5JRUq1cvAoaN+wyEQoj7zfEB4P36P8k5Qx1Q3u9zH7B/76BeC2/jJwo7x0371FfDSsYW6kJk/g6rKiVD33076w9hnF+9CRj5HyRayNo0XM+HLLVQ4Ge4mlPCoRn5YiUG3SqY4oheP2Rqxlj1CrHSgNBFwc2q7kGLhamJoCAm1+Y0ql5dSM/rp4lvoFwb0m/MFTCxPP/S/zbsKCWf2JSFtuTnBu9Y+qstCY7OlWMZF0gNqpMrMu6tV6IjfrhzaT0tXLEVn8zMRl9kt8ZNrDjQFQLxoaXPodnslhva/O4aalO9Z35IxuZxncn1HjxKw= X-Bogosity: Ham, tests=bogofilter, spamicity=0.001889, 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 Mon, May 6, 2024 at 12:18=E2=80=AFPM David Hildenbrand wrote: > > On 06.05.24 20:52, Yosry Ahmed wrote: > > On Mon, May 6, 2024 at 11:35=E2=80=AFAM David Hildenbrand wrote: > >> > >> On 06.05.24 19:00, Yosry Ahmed wrote: > >>> Do not use __lruvec_stat_mod_folio() when updating NR_FILE_PMDMAPPED = and > >>> NR_SHMEM_PMDMAPPED as these stats are not maintained per-memcg. Use > >>> __mod_node_page_state() instead, which updates the global per-node st= ats > >>> only. > >> > >> What's the effect of this? IIUC, it's been that way forever, no? > > > > Yes, but it has been the case that all the NR_VM_EVENT_ITEMS stats > > were maintained per-memcg, although some of those fields are not > > exposed anywhere. > > > > Shakeel recently added commit14e0f6c957e39 ("memcg: reduce memory for > > the lruvec and memcg stats"), which changed this such that we only > > maintain the stats we actually expose per-memcg (via a translation > > table). > > Valuable information we should add to the patch description :) > > > > > He also added commit 514462bbe927b ("memcg: warn for unexpected events > > and stats"), which warns if we try to update a stat per-memcg that we > > do not maintain per-memcg (i.e. the warning firing here). The goal is > > to make sure the translation table has all the stats it needs to have. > > > > Both of these commits were just merged today into mm-stable, hence the > > need for the fix now. It is the warning working as intended. No Fixes > > or CC stable are needed, but if necessary I would think: > > WARN* should usually be "Fixes:"d, because WARN* expresses a condition > that shouldn't be happening. > > Documentation/process/coding-style.rst contains details. > > > > > Fixes: 514462bbe927b ("memcg: warn for unexpected events and stats") > > > > , because without the warning, the stat update will just be ignored. > > So if anything the warning should have been added *after* this was > > fixed up. > > Ideally, yes. But if it's in mm-stable, we usually can no longer > reshuffle patches (commit IDs stable). I will send v2 shortly with the missing negative sign, amended commit log, and the Fixes tag. Thanks for taking a look! > -- > Cheers, > > David / dhildenb > >