linux-kernel - Re: [PATCH 1/2] mem_cgroup: optimize the atomic count of wb

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Message-ID: <03145735-7764-4cd4-e15b-60402f4b447e@gmail.com>
Date:   Fri, 24 Sep 2021 21:02:52 +0800
From:   brookxu <brookxu.cn@...il.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     hannes@...xchg.org, vdavydov.dev@...il.com,
        akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        cgroups@...r.kernel.org
Subject: Re: [PATCH 1/2] mem_cgroup: optimize the atomic count of
 wb_completion

Thanks for your time.

Michal Hocko wrote on 2021/9/24 17:34:
> On Fri 24-09-21 14:46:22, brookxu wrote:
>> From: Chunguang Xu <brookxu@...cent.com>
>>
>> In order to track inflight foreign writeback, we init
>> wb_completion.cnt to 1. For normal writeback, this cause
>> wb_wait_for_completion() to perform meaningless atomic
>> operations. Since foreign writebacks rarely occur in most
>> scenarios, we can init wb_completion.cnt to 0 and set
>> frn.done.cnt to 1. In this way we can avoid unnecessary
>> atomic operations.
> 
> Does this lead to any measurable differences?

I created multiple cgroups that performed IO on multiple disks, 
then flushed the cache with sync command, and no measurable
differences have been observed so far.

>