linux-kernel - Re: [External] Re: [PATCH] cpuset: introduce non-blocking cpuset.mems setting option

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Message-ID: <pkzbpeu7w6jc6tzijldiqutv4maft2nyfjsbmobpjfr5kkn27j@e6bflvg7mewi>
Date: Wed, 18 Jun 2025 11:04:49 +0200
From: Michal Koutný <mkoutny@...e.com>
To: Zhongkun He <hezhongkun.hzk@...edance.com>
Cc: Tejun Heo <tj@...nel.org>, Waiman Long <llong@...hat.com>, 
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org, muchun.song@...ux.dev
Subject: Re: [External] Re: [PATCH] cpuset: introduce non-blocking
 cpuset.mems setting option

On Wed, Jun 18, 2025 at 10:46:02AM +0800, Zhongkun He <hezhongkun.hzk@...edance.com> wrote:
> It is unnecessary to adjust memory affinity periodically from userspace,
> as it is a costly operation.

It'd be always costly when there's lots of data to migrate.

> Instead, we need to shrink cpuset.mems to explicitly specify the NUMA
> node from which newly allocated pages should come, and migrate the
> pages once in userspace slowly  or adjusted by numa balance.

IIUC, the issue is that there's no set_mempolicy(2) for 3rd party
threads (it only operates on current) OR that the migration path should
be optimized to avoid those latencies -- do you know what is the
contention point?

Thanks,
Michal

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