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

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Date:	Mon, 9 Mar 2015 11:07:17 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	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 (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.


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.)

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.

	-ss
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