linux-kernel - Re: [RFC 0/6] zsmalloc support compaction

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Date:	Thu, 04 Dec 2014 15:49:21 +0900
From:	"박승호/책임연구원/SW Platform(연)AOT팀(seungho1.park@....com)" 
	<seungho1.park@....com>
To:	Minchan Kim <minchan@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
CC:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Nitin Gupta <ngupta@...are.org>,
	Dan Streetman <ddstreet@...e.org>,
	Seth Jennings <sjennings@...iantweb.net>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Luigi Semenzato <semenzato@...gle.com>,
	Jerome Marchand <jmarchan@...hat.com>, juno.choi@....com
Subject: Re: [RFC 0/6] zsmalloc support compaction

Hi, Minchan.

I have a question.
The problem mentioned can't be resolved with compaction?
Is there any reason that zsmalloc pages can't be moved by compaction
operation in direct reclaim?

2014-12-02 오전 11:49에 Minchan Kim 이(가) 쓴 글:
> Recently, there was issue about zsmalloc fragmentation and
> I got a report from Juno that new fork failed although there
> are plenty of free pages in the system.
> His investigation revealed zram is one of the culprit to make
> heavy fragmentation so there was no more contiguous 16K page
> for pgd to fork in the ARM.
>
> This patchset implement *basic* zsmalloc compaction support
> and zram utilizes it so admin can do
> 	"echo 1 > /sys/block/zram0/compact"
>
> Actually, ideal is that mm migrate code is aware of zram pages and
> migrate them out automatically without admin's manual opeartion
> when system is out of contiguous page. Howver, we need more thinking
> before adding more hooks to migrate.c. Even though we implement it,
> we need manual trigger mode, too so I hope we could enhance
> zram migration stuff based on this primitive functions in future.
>
> I just tested it on only x86 so need more testing on other arches.
> Additionally, I should have a number for zsmalloc regression
> caused by indirect layering. Unfortunately, I don't have any
> ARM test machine on my desk. I will get it soon and test it.
> Anyway, before further work, I'd like to hear opinion.
>
> Pathset is based on v3.18-rc6-mmotm-2014-11-26-15-45.
>
> Thanks.
>
> Minchan Kim (6):
>    zsmalloc: expand size class to support sizeof(unsigned long)
>    zsmalloc: add indrection layer to decouple handle from object
>    zsmalloc: implement reverse mapping
>    zsmalloc: encode alloced mark in handle object
>    zsmalloc: support compaction
>    zram: support compaction
>
>   drivers/block/zram/zram_drv.c |  24 ++
>   drivers/block/zram/zram_drv.h |   1 +
>   include/linux/zsmalloc.h      |   1 +
>   mm/zsmalloc.c                 | 596 +++++++++++++++++++++++++++++++++++++-----
>   4 files changed, 552 insertions(+), 70 deletions(-)
>

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