linux-kernel - Re: [PATCH] mm: optimize stat output for 11% sys time reduce

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Message-ID: <7ia45x9bhg8c.fsf@castle.c.googlers.com>
Date: Thu, 08 Jan 2026 22:49:55 +0000
From: Roman Gushchin <roman.gushchin@...ux.dev>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Jianyue Wu <wujianyue000@...il.com>,  jianyuew@...dia.com,
  hannes@...xchg.org,  mhocko@...nel.org,  shakeel.butt@...ux.dev,
  muchun.song@...ux.dev,  linux-mm@...ck.org,  cgroups@...r.kernel.org,
  linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: optimize stat output for 11% sys time reduce

Andrew Morton <akpm@...ux-foundation.org> writes:

> On Thu,  8 Jan 2026 17:37:29 +0800 Jianyue Wu <wujianyue000@...il.com> wrote:
>
>> From: Jianyue Wu <wujianyue000@...il.com>
>> 
>> 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
>> 
>> 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)
>> 
>> 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
>> 
>
> I suspect there are workloads which read these files frequently.
>
> I'd be interested in learning "how frequently".  Perhaps
> ascii-through-sysfs simply isn't an appropriate API for this data?

We just got a bpf interface for this data merged, exactly to speed
things up: commit 99430ab8b804 ("mm: introduce BPF kfuncs to access
memcg statistics and events") in bpf-next.