linux-kernel - Re: [PATCH v18 00/32] per memcg lru

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Date:   Wed, 9 Sep 2020 13:40:57 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Aaron Lu <aaron.lwe@...il.com>
Cc:     Daniel Jordan <daniel.m.jordan@...cle.com>,
        Alex Shi <alex.shi@...ux.alibaba.com>,
        Hugh Dickins <hughd@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        mgorman@...hsingularity.net, tj@...nel.org,
        khlebnikov@...dex-team.ru, willy@...radead.org, hannes@...xchg.org,
        lkp@...el.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        cgroups@...r.kernel.org, shakeelb@...gle.com,
        iamjoonsoo.kim@....com, richard.weiyang@...il.com,
        kirill@...temov.name, alexander.duyck@...il.com,
        rong.a.chen@...el.com, vdavydov.dev@...il.com, shy828301@...il.com
Subject: Re: [PATCH v18 00/32] per memcg lru_lock

On Wed 09-09-20 10:44:32, Aaron Lu wrote:
> On Thu, Aug 27, 2020 at 09:40:22PM -0400, Daniel Jordan wrote:
> > I went back to your v1 post to see what motivated you originally, and you had
> > some results from aim9 but nothing about where this reared its head in the
> > first place.  How did you discover the bottleneck?  I'm just curious about how
> > lru_lock hurts in practice.
> 
> I think making lru_lock per-memcg helps in colocated environment: some
> workloads are of high priority while some workloads are of low priority.
> 
> For these low priority workloads, we may even want to use some swap for
> it to save memory and this can cause frequent alloc/reclaim, depending
> on its workingset etc. and these alloc/reclaim need to hold the global
> lru lock and zone lock. And then when the high priority workloads do
> page fault, their performance can be adversely affected and that is not
> acceptible since these high priority workloads normally have strict SLA
> requirement.

While this all sounds reasonably. We are lacking _any_ numbers to
actually make that a solid argumentation rather than hand waving.
Having something solid is absolutely necessary for a big change like
this.

-- 
Michal Hocko
SUSE Labs