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AJvYcCWHVF42ZdBjQDqTaOHkKtOkysqMxQy3L7dxdIxlrF9CFCHQ8Vapl7ZdWV0wpOJqkRzCeo1f0EG4/rSBI7s14fBqRgI= X-Gm-Message-State: AOJu0YzYQO0Hk2eqXXePbnlkLPzCKGy1s+u6/0ZK+AMMhrzMh9mV7p/J TzUf4IH8PfNYjp/6zvMnilDXrDCZZi062uhPpwgvhkmdlBOPjNHqkYtQM/D7hZakWmdbAc2ULJY UHQCABk98x9rXGEKTJBb+N5wWjufsczLlW5Ct X-Google-Smtp-Source: AGHT+IHLyPYvXfGlogID2l+7RlQpARx4A0v7by2uAHcT47lAr9k/vY5ZKFTIohicwN5WPwQIYzSAZXmKPR4lkQUUe/s= X-Received: by 2002:a17:907:7782:b0:a6f:56d2:8f0d with SMTP id a640c23a62f3a-a7245ba3ba8mr1149592966b.17.1719488065900; Thu, 27 Jun 2024 04:34:25 -0700 (PDT) MIME-Version: 1.0 References: <20240626094232.2432891-1-xiujianfeng@huawei.com> In-Reply-To: From: Yosry Ahmed Date: Thu, 27 Jun 2024 04:33:50 -0700 Message-ID: Subject: Re: [PATCH -next] mm: memcg: remove redundant seq_buf_has_overflowed() To: Michal Hocko Cc: Xiu Jianfeng , hannes@cmpxchg.org, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, akpm@linux-foundation.org, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: joatectwcjxqim6gr9wfppmnmxxt5mf7 X-Rspamd-Queue-Id: EA211100012 X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1719488067-132763 X-HE-Meta: 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 rLkX09hv AmNX/SBTqMbZ69XYmn3rxWOcJtJMS0t/as9LivKxLFEMRU6bqGQSzFLZvivhT7AM1Rag4Xtq6tpuBvvUjblUl9w0+iU3WuFaIMEcw3fOeSULMFQzSchyXSdd1Ds42e2cbOgI+6t+/xuvI4bVZjcg+yo6waK88SvJNX/BnSt5r9ncBpFaFUYkxSSTNZOIcPjl2D2/CNQwkGDpDUORlCsyxYOVFv+eWo0G28hgtpneyH4o+/Exl0ZBekJ/BSDdQ6djb51hhuyUjiwZfmFB/z2VLUuNbGw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.006919, 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 Thu, Jun 27, 2024 at 12:13=E2=80=AFAM Michal Hocko wro= te: > > On Wed 26-06-24 09:42:32, Xiu Jianfeng wrote: > > Both the end of memory_stat_format() and memcg_stat_format() will call > > WARN_ON_ONCE(seq_buf_has_overflowed()). However, memory_stat_format() > > is the only caller of memcg_stat_format(), when memcg is on the default > > hierarchy, seq_buf_has_overflowed() will be executed twice, so remove > > the reduntant one. > > Shouldn't we rather remove both? Are they giving us anything useful > actually? Would a simpl pr_warn be sufficient? Afterall all we care > about is to learn that we need to grow the buffer size because our stats > do not fit anymore. It is not really important whether that is an OOM or > cgroupfs interface path. Is it possible for userspace readers to break if the stats are incomplete? If yes, I think WARN_ON_ONCE() may be prompted to make it easier to catch and fix before deployment.