linux-kernel - Re: [patch 6/6] mm: memcg: print statistics from live counters

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Message-ID: <4FB43FDB.6050300@jp.fujitsu.com>
Date:	Thu, 17 May 2012 09:01:31 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>, cgroups@...r.kernel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 6/6] mm: memcg: print statistics from live counters

(2012/05/17 8:01), Andrew Morton wrote:

> On Mon, 14 May 2012 20:00:51 +0200
> Johannes Weiner <hannes@...xchg.org> wrote:
> 
>> Directly print statistics and event counters instead of going through
>> an intermediate accumulation stage into a separate array, which used
>> to require defining statistic items in more than one place.
>>
>> ...
>>
>> -static const char *memcg_stat_strings[NR_MCS_STAT] = {
>> -	"cache",
>> -	"rss",
>> -	"mapped_file",
> 
> Bah humbug, who went and called this mapped_file?
> 
> This stat is derived from MEM_CGROUP_STAT_FILE_MAPPED.  But if we
> rename MEM_CGROUP_STAT_FILE_MAPPED to MEM_CGROUP_STAT_MAPPED_FILE then
> we also need to rename the non-memcg NR_FILE_MAPPED.  And we can't
> change the text to "file_mapped" because it's ABI.
> 


Sorry..

>> -	"mlock",
>> -	"swap",
> 
> And "swap" is derived from MEM_CGROUP_STAT_SWAPOUT.  We could rename
> that to MEM_CGROUP_STAT_SWAP without trouble.
> 

Yes.

> But both are poor names.  There are two concepts here: a) swapout
> events (ie: swap writeout initiation) and b) swapspace usage.  Type a)
> only ever counts up, whereas type b) counts up and down.
> 
> MEM_CGROUP_STAT_SWAPOUT is actually of type b), but "swapout" is a
> misleading term, because it refers to type a) events.
> 

I'll prepare a patch.

> And the human-displayed "swap" is useless because it can refer to
> either type a) or type b) events.  These should be called "swapped" and
> MEM_CGROUP_STAT_SWAPPED.  But we can't change the userspace interface.
> 
> argh, I hate you all!
> 

Hm...sorry. I(fujitsu) am now considering to add meminfo for memcg...,

add an option to override /proc/meminfo if a task is in container or
meminfo file somewhere.
(Now, we cannot trust /usr/bin/free, /usr/bin/top etc...in a container.)

so...I think usual user experience will be better because of the same format
with meminfo.

Thanks,
-Kame


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