linux-kernel - Re: [PATCH v4] mm: oom: introduce cpuset oom

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Date:   Thu, 17 Aug 2023 12:45:43 -0400
From:   Waiman Long <longman@...hat.com>
To:     Gang Li <gang.li@...ux.dev>, Michal Hocko <mhocko@...e.com>
Cc:     cgroups@...r.kernel.org, linux-mm@...ck.org, rientjes@...gle.com,
        Zefan Li <lizefan.x@...edance.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] mm: oom: introduce cpuset oom

On 8/17/23 04:40, Gang Li wrote:
>
> Since __GFP_HARDWALL is set as long as cpuset is enabled, I think we can
> use it to determine if we are under the constraint of CPUSET.
>
> But I have a question: Why we always set __GFP_HARDWALL when cpuset is
> enabled, regardless of the value of cpuset.mem_hardwall?

There is no direct dependency between cpuset.mem_hardwall and the 
__GFP_HARDWALL flag. When cpuset is enabled, all user memory allocation 
should be subjected to the cpuset memory constraint. In the case of 
non-user memory allocation, it can fall back to to the node mask of an 
ancestor up to the root cgroup, i.e. all memory nodes. 
cpuset.mem_hardwall enables a barrier to this upward search.

Note that cpuset.mem_hardwall is a v1 feature that is not available in 
cgroup v2.

Cheers,
Longman