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From:   Waiman Long <llong@redhat.com>
Subject: Re: [PATCH v3 0/5] mm/memcg: Reduce kmemcache memory accounting
 overhead
To:     Matthew Wilcox <willy@infradead.org>
Cc:     Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Tejun Heo <tj@kernel.org>, Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Vlastimil Babka <vbabka@suse.cz>, Roman Gushchin <guro@fb.com>,
        linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
        linux-mm@kvack.org, Shakeel Butt <shakeelb@google.com>,
        Muchun Song <songmuchun@bytedance.com>,
        Alex Shi <alex.shi@linux.alibaba.com>,
        Chris Down <chris@chrisdown.name>,
        Yafang Shao <laoar.shao@gmail.com>,
        Wei Yang <richard.weiyang@gmail.com>,
        Masayoshi Mizuma <msys.mizuma@gmail.com>,
        Xing Zhengjun <zhengjun.xing@linux.intel.com>
References: <20210414012027.5352-1-longman@redhat.com>
 <20210415171035.GB2531743@casper.infradead.org>
Message-ID: <15cf3cfa-c221-9e84-9f5b-80082207efd3@redhat.com>
Date:   Thu, 15 Apr 2021 13:41:07 -0400
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On 4/15/21 1:10 PM, Matthew Wilcox wrote:
> On Tue, Apr 13, 2021 at 09:20:22PM -0400, Waiman Long wrote:
>> With memory accounting disable, the run time was 2.848s. With memory
>> accounting enabled, the run times with the application of various
>> patches in the patchset were:
>>
>>    Applied patches   Run time   Accounting overhead   Overhead %age
>>    ---------------   --------   -------------------   -------------
>>         None          10.800s         7.952s              100.0%
>>          1-2           9.140s         6.292s               79.1%
>>          1-3           7.641s         4.793s               60.3%
>>          1-5           6.801s         3.953s               49.7%
> I think this is a misleading way to report the overhead.  I would have said:
>
> 			10.800s		7.952s		279.2%
> 			 9.140s		6.292s		220.9%
> 			 7.641s		4.793s		168.3%
> 			 6.801s		3.953s		138.8%
>
What I want to emphasize is the reduction in the accounting overhead 
part of execution time. Your percentage used the accounting disable time 
as the denominator. I think both are valid, I will be more clear about 
that in my version of the patch.

Thanks,
Longman