linux-kernel - Re: what's cooking in zram for 4.1

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Message-ID: <20150518144027.GA10979@swordfish>
Date:	Mon, 18 May 2015 23:40:27 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Karel Zak <kzak@...hat.com>,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	linux-kernel@...r.kernel.org, util-linux@...r.kernel.org
Subject: Re: what's cooking in zram for 4.1

On (05/18/15 22:55), Minchan Kim wrote:
> > > Why do you need all in one file? ... to provide consistent statistics?
> > > 
> > 
> > yes, that's the main reason.
> 
> In my side, other main reason was to reduce the number of system call
> to see statistics. It is not only syscall overhead itself but also
> causes slightly high-order allocation for kernel internal data structure
> via slab allocation which is bad on low memory situation where is
> frequent in zram-swap. Slab allocation could be fallback with 0-order
> pages but it could cause excessive page reclaim seriously since compaction
> didn't work.
> Yes, it's a one of problem of current VM but there is no reason to hesitate
> if we can avoid such problems and support consistent statistic as well.
> 

true.

syscalls and corresponding error handling for each one of them were on a
list:
https://www.marc.info/?l=linux-kernel&m=142586445420298&w=2

Karel has a remarkably good codebase, so error handling would not be an
issue :-) that's why consistent stats moved forward.

in general, increasing consistency and reducing the syscall pressure are
good enough to move on.

	-ss
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