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

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Date:	Mon, 9 Mar 2015 11:21:27 +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 11:07:17AM +0900, Sergey Senozhatsky wrote:
> On (03/09/15 10:47), Minchan Kim wrote:
> > > > 
> > > > It's not enough. What I want to know is compaction efficiency per client of
> > > > zsmalloc(ie, zram). 
> > > >
> > > 
> > > so what a typical user can do with this information? isn't it an entirely
> > > debug info that makes some hidden sense only to developers?
> > 
> > Absolutely true.
> > 
> > > 
> > > if you insist on exporting this as a zram stat for everyone how obout
> > > starting to move away from per-stat RO sysfs attrs. it seems that we have
> > > uncomfortably a lot of sysfs attrs, and that doesn't make life easier in
> > > user space. for example, block devices have /sys/block/.../stat file:
> > > 
> > > /sys/block/sda$ cat stat
> > >    45931       59  2075686   289906    55768     9229  1967800   318033        0   193583   607806
> > > 
> > > and there are no num_reads, num_writes, num_failed_reads, num_failed_writes,
> > > etc., etc. per-stat sysfs attrs force user-space to do lots of syscalls:
> > > open(), read(), close() with error control on every step; for every stat.
> > 
> > I absoulte agree with you and I really wanted to tidy it up but was no
> > time. Sergey, Could you contribute? If you have no time, I will do by
> > myself but it would be low priority now.
> 
> sure. I can handle it.

Thanks!

> 
> 
> I was thinking for some time already about splitting stats that we
> export in two categories and, thus, two files: IO_stats and MM_stats.
> 
> zram<id>/io_stat
> 
> s*printf( num_reads, num_writes, failed_reads, failed_writes, etc.)

Some of it(ie, num_reads, num_writes) was duplicated with /dev/block/zramx/stat?
I know /dev/block/zramx/stat doesn't work now and I didn't check why it doesn't
work but I hope we make it work so remove duplicate stat, finally. :)

> 
> zram<id>/mm_stat
> s*printf( orig_data_size, compr_data_size, mem_used_total, num_migrated, etc.)
> 
> 
> 
> so hoprefully in several years we can entirely remove ZRAM_ATTR_RO functions.
> probably, first moving them under #ifdef CONFIG_OLD_ZRAM_STATS at some point
> in the future.

Sounds good so we could warn for 1 or 2 years if users are about to use old stat
and finally removes deprecated stat.
Please Cc util-linux zram-control peoples when you send patchset.

> 
> 	-ss

-- 
Kind regards,
Minchan Kim
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