linux-kernel - Re: [PATCH v4 01/13] mm: Assign id to every memcg-aware shrinker

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Date:   Thu, 10 May 2018 12:42:37 +0300
From:   Kirill Tkhai <ktkhai@...tuozzo.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     vdavydov.dev@...il.com, shakeelb@...gle.com,
        viro@...iv.linux.org.uk, hannes@...xchg.org, mhocko@...nel.org,
        tglx@...utronix.de, pombredanne@...b.com, stummala@...eaurora.org,
        gregkh@...uxfoundation.org, sfr@...b.auug.org.au, guro@...com,
        mka@...omium.org, penguin-kernel@...ove.SAKURA.ne.jp,
        chris@...is-wilson.co.uk, longman@...hat.com, minchan@...nel.org,
        ying.huang@...el.com, mgorman@...hsingularity.net, jbacik@...com,
        linux@...ck-us.net, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, willy@...radead.org, lirongqing@...du.com,
        aryabinin@...tuozzo.com
Subject: Re: [PATCH v4 01/13] mm: Assign id to every memcg-aware shrinker

On 10.05.2018 01:55, Andrew Morton wrote:
> On Wed, 09 May 2018 14:56:55 +0300 Kirill Tkhai <ktkhai@...tuozzo.com> wrote:
> 
>> The patch introduces shrinker::id number, which is used to enumerate
>> memcg-aware shrinkers. The number start from 0, and the code tries
>> to maintain it as small as possible.
>>
>> This will be used as to represent a memcg-aware shrinkers in memcg
>> shrinkers map.
>>
>> ...
>>
>> --- a/fs/super.c
>> +++ b/fs/super.c
>> @@ -248,6 +248,9 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags,
>>  	s->s_time_gran = 1000000000;
>>  	s->cleancache_poolid = CLEANCACHE_NO_POOL;
>>  
>> +#if defined(CONFIG_MEMCG) && !defined(CONFIG_SLOB)
> 
> It would be more conventional to do this logic in Kconfig - define a
> new MEMCG_SHRINKER which equals MEMCG && !SLOB.
> 
> This ifdef occurs a distressing number of times in the patchset :( I
> wonder if there's something we can do about that.
> 
> Also, why doesn't it work with slob?  Please describe the issue in the
> changelogs somewhere.

All currently existing memcg-aware shrinkers are based on list_lru, which
does not introduce separate memcg lists for SLOB case. So, the optimization
made by this patchset is not need there.

I'll make MEMCG_SHRINKER in next version like you suggested. Even if we have
no such shrinkers at the moment, we may have them in the future, and this will
be useful anyway.
 
> It's a pretty big patchset.  I *could* merge it up in the hope that
> someone is planning do do a review soon.  But is there such a person?

Thanks,
Kirill