linux-kernel - Re: [PATCH 0/6] new zram statistics reporting scheme

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Date:	Thu, 12 Mar 2015 14:11:15 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nitin Gupta <ngupta@...are.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/6] new zram statistics reporting scheme

On Thu, Mar 12, 2015 at 11:16:09AM +0900, Sergey Senozhatsky wrote:
> On (03/12/15 10:55), Minchan Kim wrote:
> > I really appreciate you enhance stat functions, esp, working with iostat!
> 
> thanks! my pleasure.
> 
> > One thing I want to discuss is sometime we could remove RO fields
> > in /sys/block/zram/ but we couldn't remove RW fields because
> > io_stat/mm_stat doesn't have any writable option now so users will
> > have two options to read stat. For exmaple,
> 
> I played with CONFIG_ZRAM_OLD_STATS option, which turns RW attrs into
> WO attrs (where possible/needed). but it turned out to be a rather
> ugly patch and I eventually decided that I don't want to have these
> #ifdef-s in zram code for the next two years. so providing both RW/RO
> old stats (with a warning in the logs) and RO [mm|io]_stat sound like
> a better plan.

I think we don't need CONFIG_ZRAM_OLD_STATS.
For example, for mem_used_max, we could add pr_warn_once in
*mem_used_max_show* but not *mem_used_max_store*. so, old users will see
deprecated message when they try to *read* the vaule old stat while they
will write new value.
One or two year later, we could remove mem_used_max_show then everyone
should read the vaule /sys/block/zram0/mm_stat.

> 
> >         cat /sys/block/zram/mem_used_max
> >         cat /sys/block/zram/mm_stat | awk friend
> > 
> > How about changing only writeable, not readable for duplicated stats
> > in /sys/block/zram? So, user will have writeable stat to set some
> > options in /sys/block/zram and readable stat to get some data in
> > /sys/block/zram/[io|mm]_stat if the stat is duplicated in both.
> 
> Sorry, I probably didn't drink enough coffee today, can you please
> rephrase or give a trivial example?

Sorry, I was vague. I meant users can read the vaule for
mem_used_max and mem_limit in two places(ie, /sys/block/zram/
and /sys/block/zram/mm_stat). If we feel it's handy for user,
i am not against that. But if there is no reason, I want to
make /sys/block/zram/ stat write-only if it is possible stat
like mem_used_max. I guess It's easier rule for user.


> 
> 		-ss

-- 
Kind regards,
Minchan Kim
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