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[195.250.132.146]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-584d16bbc23sm740841a12.52.2024.06.27.04.20.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 27 Jun 2024 04:20:55 -0700 (PDT) Date: Thu, 27 Jun 2024 13:20:55 +0200 From: Michal Hocko To: xiujianfeng Cc: 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=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: CBD58C0011 X-Stat-Signature: b8oypy6uedeytjoow8ttmduu81p6cyk6 X-HE-Tag: 1719487259-120831 X-HE-Meta: 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 k6GYo/rN vPqM1uDFqHpyYDmGqakAt07afH43znUKTkruyIth9tkoF2xlMKEs5IQeA87lfuibUD7RPo1GqHjcTGeMzfiG3ifvWOrQghDtbYQsIrLrvb43noSxG3ExvU/Z7kgq7thodBjhekwpIBU/8NGibkiP/F/JWLv5IT4jLwmxCfcJJhBBx48dV9afG2L+gMzcsurYQchlre7alAPMu5WMkzzRjsVXSgxZISdV6bL+1WoegDN4ja2rm5wd7DIe2gnbVTv0OP/wMj3GeNCLlHwWSorFOlhc9+FDEv8S5c9JjQxs6E44QtwwaYscbrtHWfWcqWmcSVkXTkEswuLj3nxo= X-Bogosity: Ham, tests=bogofilter, spamicity=0.001513, 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 16:33:00, xiujianfeng wrote: > > > On 2024/6/27 15:13, 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. > > I did a test, when I removed both of them and added a lot of prints in > memcg_stat_format() to make the seq_buf overflow, and then cat > memory.stat in user mode, no OOM occurred, and there were no warning > logs in the kernel. The default buffer size is PAGE_SIZE. -- Michal Hocko SUSE Labs