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

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Message-ID: <20220112002551.sksmoril2nwuddtu@master>
Date:   Wed, 12 Jan 2022 00:25:51 +0000
From:   Wei Yang <richard.weiyang@...il.com>
To:     Roman Gushchin <guro@...com>
Cc:     Wei Yang <richard.weiyang@...il.com>, 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 10:23:41AM -0800, Roman Gushchin wrote:
>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).

Usually the size is small I think.

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

Yep.

>
>Thanks!

-- 
Wei Yang
Help you, Help me