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Date: Wed, 20 Dec 2017 16:15:00 +0900
From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Subject: Re: [PATCH v2] mm/zsmalloc: simplify shrinker init/destroy
Message-ID: <20171220071500.GA11774@jagdpanzerIV>
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To: Michal Hocko <mhocko@kernel.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>, Aliaksei Karaliou <akaraliou.dev@gmail.com>, minchan@kernel.org, ngupta@vflare.org, sergey.senozhatsky.work@gmail.com, linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>

Hi,

On (12/19/17 16:58), Michal Hocko wrote:
[..]
> > we use shrinker for "optional" de-fragmentation of zsmalloc pools. we
> > don't free any objects from that path. just move them around within their
> > size classes - to consolidate objects and to, may be, free unused pages
> > [but we first need to make them "unused"]. it's not a mandatory thing for
> > zsmalloc, we are just trying to be nice.
> 
> OK, it smells like an abuse of the API

we don't use shrinker callback to "just reduce the internal fragmentation".
the only reason we do de-fragmentation is to release the pages. if we see
that defragmentation is going to be a useless exercise and we are not going
to free pages, we just skip that class.

so at the end it's - the kernel asks us to shrink, we are trying to shrink
[release unneeded pages].

	-ss

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