linux-kernel - Re: + zram-support-compaction.patch added to -mm tree

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Date:	Mon, 9 Mar 2015 10:05:22 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:	akpm@...ux-foundation.org, ddstreet@...e.org, gunho.lee@....com,
	iamjoonsoo.kim@....com, jmarchan@...hat.com, juno.choi@....com,
	mel@....ul.ie, ngupta@...are.org, semenzato@...gle.com,
	sergey.senozhatsky@...il.com, sjennings@...iantweb.net,
	mm-commits@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: + zram-support-compaction.patch added to -mm tree

On Mon, Mar 09, 2015 at 09:57:18AM +0900, Sergey Senozhatsky wrote:
> On (03/09/15 09:49), Minchan Kim wrote:
> > > rather a discussion question.
> > > 
> > > Minchan, do you want to provide num_migrated as part of zsmalloc stats rather
> > > than having yet another zram attr? we already provide zsmalloc stats and this
> > > type of information seems to belong there. just idea.
> > 
> > Hmm, CONFIG_ZSMALLOC_STAT is actually to show zsmalloc internals.
> 
> well, to be fair, compaction is a zsmalloc internal. zram has nothing to do with
> it.
> 
> but do we we even need this stat? it seems that
> 
>    mem_total_used (before compaction) - mem_total_user (after comapction)
> 
> will give user an idea on how much memory was compacted.

It's not enough. What I want to know is compaction efficiency per client of
zsmalloc(ie, zram). IOW, (how many of freed pages / how many of objects) per
zs_compact.

> 
> 	-ss
> 
> > That's why it is on debugfs. If we add the stat into zsmalloc, we should turn on debugfs
> > and CONFIG_ZSMALLOC_STAT to see *a* stat. Even, CONFIG_ZSMALLOC_STAT will add
> > unncessary overheads to account another stats fo zsmalloc internals.
> > 
> > As well, if we add auto-compacion like stuff in zsmalloc(ie, it will trigger
> > by itself if fragmention is over to predefined theshold), the stat will
> > accumulate stat while someone want to see snapshot compaction effiecieny
> > of the moment.
> > 
> > So, I want to keep it in zram now.
> > 
> > -- 
> > Kind regards,
> > Minchan Kim
> > 

-- 
Kind regards,
Minchan Kim
--
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