linux-kernel - Re: [PATCH] zsmalloc: consider ZS_ALMOST

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Date:	Fri, 10 Jul 2015 14:34:41 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Nitin Gupta <ngupta@...are.org>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH] zsmalloc: consider ZS_ALMOST_FULL as migrate source

On (07/10/15 14:21), Minchan Kim wrote:
> > I mean I find your argument that some level of fragmentation
> > can be of use to be valid, to some degree.
> 
> The benefit I had in mind was to prevent failure of allocation.
> 

Sure. I tested the patch.

cat /sys/block/zram0/mm_stat
3122102272 2882639758 2890366976        0 2969432064       55    79294

cat /sys/block/zram0/stat
    7212        0    57696       73  7513254        0 60106032    52096     0    52106    52113

Compaction stats:

[14637.002961] compaction nr:89 (full:528 part:3027)  ~= 0.148

Nothing `alarming'.


> > I'm thinking now, does it make sense to try harder here? if we
> > failed to alloc_zspage(), then may be we can try any of unused
> > objects from a 'upper' (larger/next) class?  there might be a
> > plenty of them.
> 
> I actually thought about that but I didn't have any report from
> community and product division of my compamy until now.
> But with auto-compaction, the chance would be higher than old
> so let's keep an eye on it(I think users can find it easily because
> swap layer emits "write write failure").
> 
> If it happens(ie, any report from someone), we could try to compact
> and then if it fails, we could fall back to upper class as a last
> resort.
> 

OK.

	-ss
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