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[195.250.132.146]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-584d17b03f3sm779936a12.47.2024.06.27.04.56.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 27 Jun 2024 04:56:51 -0700 (PDT) Date: Thu, 27 Jun 2024 13:56:51 +0200 From: Michal Hocko To: Yosry Ahmed 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 Subject: Re: [PATCH -next] mm: memcg: remove redundant seq_buf_has_overflowed() Message-ID: References: <20240626094232.2432891-1-xiujianfeng@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: AF8C9C0002 X-Stat-Signature: ztkx5qc9ksptz6xmcqyoszactiyoym7d X-Rspam-User: X-HE-Tag: 1719489413-300151 X-HE-Meta: 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 W80ehGc8 +WoVqZPKuLOIZR1nxtAk3dMPnKW2EUOxfrdJTgcoEWqocgsJWpEF4ZIKb+e/Nu5/DEmFSiDueLMwYiEZup/eGiYPapGHz4laSy0yq+4er2CtwAIx6cbwlWWgtHGrg7rWVVyI3VwqfE2mI3ntRA4NPa/Yq9wpGyFxGf/pbP4xDH4WCkA2RDMWVpStt+gFxIB7KNNKqewQSkGqTp5eXmVzvItuyPIIuriY3vDPUjrMpCv/AR5gyBJ/qKq9gFkcL9AeW4m160EVEW8xgK9+K2Izo/4arh9Naw2ZHZpEeC7mkUhVvjT3+JdIebprpbGLyRAskGfBctUcR6rMvU9gtxn254rwc5tG3PQQbgDaJ6mqUwxWG7FTa/ASJs51jKyUdIJ+Xo32OZYOlKJd38smh1X2ecX5TZYp+0ChgVDy3 X-Bogosity: Ham, tests=bogofilter, spamicity=0.002733, 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 27-06-24 04:33:50, Yosry Ahmed wrote: > On Thu, Jun 27, 2024 at 12:13 AM Michal Hocko wrote: > > > > 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? They will certainly get an imprecise picture. Sufficient to break I dunno. > If yes, I think WARN_ON_ONCE() may be prompted to make it > easier to catch and fix before deployment. The only advantage of WARN_ON_ONCE is that the splat is so verbose that it gets noticed. And also it panics the system if panic_on_warn is enabled. I do not particularly care about the latter but to me it seems like the warning is just an over reaction and a simple pr_warn should just achieve the similar effect - see my other reply -- Michal Hocko SUSE Labs