linux-kernel - Re: [PATCH mm-new v3] mm/memcontrol: Add memory.stat

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Message-ID: <061cdd9e-a70b-4d45-909a-6d50f4da8ef3@redhat.com>
Date: Tue, 11 Nov 2025 15:44:07 -0500
From: Waiman Long <llong@...hat.com>
To: Michal Hocko <mhocko@...e.com>, Waiman Long <llong@...hat.com>
Cc: Leon Huang Fu <leon.huangfu@...pee.com>, linux-mm@...ck.org,
 tj@...nel.org, mkoutny@...e.com, hannes@...xchg.org,
 roman.gushchin@...ux.dev, shakeel.butt@...ux.dev, muchun.song@...ux.dev,
 akpm@...ux-foundation.org, joel.granados@...nel.org, jack@...e.cz,
 laoar.shao@...il.com, mclapinski@...gle.com, kyle.meyer@....com,
 corbet@....net, lance.yang@...ux.dev, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, cgroups@...r.kernel.org
Subject: Re: [PATCH mm-new v3] mm/memcontrol: Add memory.stat_refresh for
 on-demand stats flushing


On 11/11/25 2:47 PM, Michal Hocko wrote:
> On Tue 11-11-25 14:10:28, Waiman Long wrote:
> [...]
>>> +static void memcg_flush_stats(struct mem_cgroup *memcg, bool force)
>>> +{
>>> +	if (mem_cgroup_disabled())
>>> +		return;
>>> +
>>> +	memcg = memcg ?: root_mem_cgroup;
>>> +	__mem_cgroup_flush_stats(memcg, force);
>>> +}
>> Shouldn't we impose a limit in term of how frequently this
>> memcg_flush_stats() function can be called like at most a few times per
> This effectivelly invalidates the primary purpose of the interface to
> provide a method to get as-fresh-as-possible value AFAICS.
>
>> second to prevent abuse from user space as stat flushing is expensive? We
>> should prevent some kind of user space DoS attack by using this new API if
>> we decide to implement it.
> What exactly would be an attack vector?

just repeatedly write a string to the new cgroup file. It will then call 
css_rstat_flush() repeatedly. It is not a real DoS attack, but it can 
still consume a lot of cpu time and slow down other tasks.

Cheers,
Longman