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AJvYcCX34HzNHzocYW0+hzBFSJPkA2Yr/Y4gy9TYKRIITD5D3B423I4ue4d8l8Y9m4sJeD0yWBeSnpegYD73xB+9hVobMyM= X-Gm-Message-State: AOJu0YwTA86cDPWBz6eOm/c5nVBkwe30O1YKrkaopMgtmX+8iFqhWx9M eKmAGPkr55Jx2SP23jY1HYrmx8eA/n7xj1NDeFQ2GLJgcd1JNQlnmjKkF2lzJE9HnIQoUpEQ3aa wJxavaczlu07+JaAhJrZD8XV9ONcVgYWykDSR X-Google-Smtp-Source: AGHT+IHrFjX5wTmKi7PvniaysCkDbK8sy8DKFkZ1UTsDu9YwftHSAjROVe4NnE5YpzMZ3uQIIP5NMmN0u2N+0w0uihw= X-Received: by 2002:a17:906:7f03:b0:a52:6435:ef09 with SMTP id d3-20020a1709067f0300b00a526435ef09mr2951843ejr.76.1714179532735; Fri, 26 Apr 2024 17:58:52 -0700 (PDT) MIME-Version: 1.0 References: <20240427003733.3898961-1-shakeel.butt@linux.dev> <20240427003733.3898961-6-shakeel.butt@linux.dev> In-Reply-To: <20240427003733.3898961-6-shakeel.butt@linux.dev> From: Yosry Ahmed Date: Fri, 26 Apr 2024 17:58:16 -0700 Message-ID: Subject: Re: [PATCH v2 5/7] memcg: pr_warn_once for unexpected events and stats To: Shakeel Butt Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Stat-Signature: rcp16srzixzdkmaenru8nd18pjupz8wn X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 7004C180006 X-HE-Tag: 1714179534-975769 X-HE-Meta: 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 qEqqUDRH +JFEcHqPdaKJYF/ou6tWiVz+lJhN0dKVKszMvb9mRPsLc15MITiMpoQnZbFi0B79IxCkgKGaWrhdfLfNoZ+IBO3FdIHwxD3ddMkpZwCHWkyPNkjT4EMT2B8QAkyQb6C9SOIPssd9uaFmtQJc6q9Ca0tkSOTSW6e5Y0+RE9352cCwAv8hofNRTpKj8JU3+IRybjm1yRFUIBZ5YZtn4Wk6GWDAPBon2ARG3a1iSQ1XaHfbRBz6bn6uWbYjaI42Lcq6PB304nqBFiMS2gwQ= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000052, 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, Apr 26, 2024 at 5:38=E2=80=AFPM Shakeel Butt wrote: > > To reduce memory usage by the memcg events and stats, the kernel uses > indirection table and only allocate stats and events which are being > used by the memcg code. To make this more robust, let's add warnings > where unexpected stats and events indexes are used. > > Signed-off-by: Shakeel Butt > --- > mm/memcontrol.c | 43 ++++++++++++++++++++++++++++++++++--------- > 1 file changed, 34 insertions(+), 9 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 103e0e53e20a..36145089dcf5 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -671,9 +671,11 @@ unsigned long lruvec_page_state(struct lruvec *lruve= c, enum node_stat_item idx) > return node_page_state(lruvec_pgdat(lruvec), idx); > > i =3D memcg_stats_index(idx); > - if (i >=3D 0) { > + if (likely(i >=3D 0)) { > pn =3D container_of(lruvec, struct mem_cgroup_per_node, l= ruvec); > x =3D READ_ONCE(pn->lruvec_stats->state[i]); > + } else { > + pr_warn_once("%s: stat item index: %d\n", __func__, idx); > } Can we make these more compact by using WARN_ON_ONCE() instead: if (WARN_ON_ONCE(i < 0)) return 0; I guess the advantage of using pr_warn_once() is that we get to print the exact stat index, but the stack trace from WARN_ON_ONCE() should make it obvious in most cases AFAICT. No strong opinions either way.