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b=vVvwcwn7p2eSF8OAMa7tYkMn2kTkDU/wPhaNdoQeovpIeSndvlEMTIfKF7OgArV1j qCwF4mUnFifje2mTXdum7upR7dZSnWm+Tt5Md5YEmTBtT4SyYPn1JbB53Q68xYIo9r Hsze7rW0ouJRsMqAxWIlCC1LYhSwc9ceYZvNUKVA= Date: Thu, 22 Jan 2026 09:13:51 -0800 From: Andrew Morton To: Jianyue Wu Cc: shakeel.butt@linux.dev, hannes@cmpxchg.org, mhocko@kernel.org, roman.gushchin@linux.dev, muchun.song@linux.dev, linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] mm: optimize stat output for 11% sys time reduce Message-Id: <20260122091351.0cc1afd5d419fafa1d98b32f@linux-foundation.org> In-Reply-To: <20260122114242.72139-1-wujianyue000@gmail.com> References: <20260110042249.31960-1-jianyuew@nvidia.com> <20260122114242.72139-1-wujianyue000@gmail.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 7F242A0003 X-Stat-Signature: k7cb7qr1gcartumiebcx1kxeb8fmtao4 X-Rspam-User: X-HE-Tag: 1769102033-232400 X-HE-Meta: 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, 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, 22 Jan 2026 19:42:42 +0800 Jianyue Wu wrote: > Replace seq_printf/seq_buf_printf with lightweight helpers to avoid > printf parsing in memcg stats output. > > Key changes: > - Add memcg_seq_put_name_val() for seq_file "name value\n" formatting > - Add memcg_seq_buf_put_name_val() for seq_buf "name value\n" formatting > - Update __memory_events_show(), swap_events_show(), > memory_stat_format(), memory_numa_stat_show(), and related helpers > - Introduce local variables to improve readability and reduce line length > > Performance: > - 1M reads of memory.stat+memory.numa_stat > - Before: real 0m9.663s, user 0m4.840s, sys 0m4.823s > - After: real 0m9.051s, user 0m4.775s, sys 0m4.275s (~11.4% sys drop) So the tl;dr here is "vfprintf() is slow". It's quite a large change, although not a complex one. Do we need to change so much? Would some subset of these changes provide most of the benefit? It does rather uglify things so there's a risk that helpful people will send "cleanups" which switch back to using *printf*. Explanatory code comments would help prevent that but we'd need a lot of them. I dunno, what do people think? Does the benefit justify the change? > Tests: > - Script: > for ((i=1; i<=1000000; i++)); do > : > /dev/null < /sys/fs/cgroup/memory.stat > : > /dev/null < /sys/fs/cgroup/memory.numa_stat > done