linux-kernel - Re: [PATCH 4/4] mm/memcg: refine mem_cgroup_threshold_ary->current

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Date:   Tue, 11 Jan 2022 10:23:41 -0800
From:   Roman Gushchin <guro@...com>
To:     Wei Yang <richard.weiyang@...il.com>
CC:     <hannes@...xchg.org>, <mhocko@...nel.org>,
        <vdavydov.dev@...il.com>, <akpm@...ux-foundation.org>,
        <shakeelb@...gle.com>, <vbabka@...e.cz>, <willy@...radead.org>,
        <songmuchun@...edance.com>, <shy828301@...il.com>,
        <surenb@...gle.com>, <linux-kernel@...r.kernel.org>,
        <cgroups@...r.kernel.org>, <linux-mm@...ck.org>
Subject: Re: [PATCH 4/4] mm/memcg: refine
 mem_cgroup_threshold_ary->current_threshold calculation

On Tue, Jan 11, 2022 at 01:03:02AM +0000, Wei Yang wrote:
> mem_cgroup_threshold_ary->current_threshold points to the last entry
> who's threshold is less or equal to usage.
> 
> Instead of iterating entries to get the correct index, we can leverage
> primary->current_threshold to get it. If the threshold added is less or
> equal to usage, current_threshold should increase by one. Otherwise, it
> doesn't change.

How big is usually an array of thresholds? If it's not huge, likely
any savings won't be really noticeable (it's not a hot path and there
is an rc_synchronize() below).

So I agree with Michal that a better justification is really needed.

Thanks!