linux-kernel - Re: [RFC PATCH v4 0/3] memcg weighted interleave mempolicy control

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Message-ID: <ZVOn2T_Qg_NTKlB2@tiehlicka>
Date:   Tue, 14 Nov 2023 18:01:13 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Gregory Price <gregory.price@...verge.com>
Cc:     "tj@...nel.org" <tj@...nel.org>, John Groves <john@...alactic.com>,
        Gregory Price <gourry.memverge@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-cxl@...r.kernel.org" <linux-cxl@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "ying.huang@...el.com" <ying.huang@...el.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "lizefan.x@...edance.com" <lizefan.x@...edance.com>,
        "hannes@...xchg.org" <hannes@...xchg.org>,
        "corbet@....net" <corbet@....net>,
        "roman.gushchin@...ux.dev" <roman.gushchin@...ux.dev>,
        "shakeelb@...gle.com" <shakeelb@...gle.com>,
        "muchun.song@...ux.dev" <muchun.song@...ux.dev>,
        "jgroves@...ron.com" <jgroves@...ron.com>
Subject: Re: [RFC PATCH v4 0/3] memcg weighted interleave mempolicy control

On Tue 14-11-23 10:50:51, Gregory Price wrote:
> On Tue, Nov 14, 2023 at 10:43:13AM +0100, Michal Hocko wrote:
[...]
> > That being said, I still believe that a cgroup based interface is a much
> > better choice over a global one. Cpusets seem to be a good fit as the
> > controller does control memory placement wrt NUMA interfaces.
> 
> I think cpusets is a non-starter due to the global spinlock required when
> reading informaiton from it:
> 
> https://elixir.bootlin.com/linux/latest/source/kernel/cgroup/cpuset.c#L391

Right, our current cpuset implementation indeed requires callback lock
from the page allocator. But that is an implementation detail. I do not
remember bug reports about the lock being a bottle neck though. If
anything cpusets lock optimizations would be win also for users who do
not want to use weighted interleave interface.
-- 
Michal Hocko
SUSE Labs