linux-kernel - Re: [Xen-devel] Re: [PATCH 7/9] blkio-cgroup-v9: Page tracking hooks

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Message-Id: <20090724151923.986dd932.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 24 Jul 2009 15:19:23 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Ryo Tsuruta <ryov@...inux.co.jp>
Cc:	xen-devel@...ts.xensource.com,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org, dm-devel@...hat.com,
	agk@...hat.com
Subject: Re: [Xen-devel] Re: [PATCH 7/9] blkio-cgroup-v9: Page tracking
 hooks

On Fri, 24 Jul 2009 14:44:16 +0900 (JST)
Ryo Tsuruta <ryov@...inux.co.jp> wrote:
 good solution to resolve such problem.
> 
> > My point is "don't allow anyone to use bandwidth of others."
> > Considering job isolation, a thread who requests swap-out should be charg=
> > ed
> > against bandwidth.
> 
> From another perspective, the swap-out is caused since the buggy
> process uses a large amount of memory, so it can be considered as 
> the bandwidth of logging process is used due to the buggy process.
> 
> Please consider the following case. If a thread who requests swap-out
> is charged, the thread is charged other threads' I/O.
> 
>    (1)                          --------      (2)
>    Process A                   |        |     Process B
>    mmaps a large area in   --> | memory | <-- tries to allocate a page.
>    the memory and writes       |        |
>    data to there.               --------     (3)
>                                    |         To get a free page,
>                                    |         the data written by Proc.A
>                                    |         is written out to the disk.
>                                    V         The I/O is done by using
>                                 ---------    Proc.B's bandwidth.
>                                |  disk   |   
>                                 ---------
> 
> Thus I think that page owners should be charged against bandwidth.
> 
Ok, no good way. yours is wrong, mine is wrong, too.
plz find 3rd way, reasonable.

Below is brief thinking.

"Why process A should be charged to I/O when it just maps anon memory ?"
I can't answer this.

Even in yorr case, Process B requests memory and get penalty. It's
very natural, I think.

In usual case, 
 - if process A maps ANON, there will be no I/O.
 - if process A maps FILE, it will be charged to process A.
ok ?

Under memory pressure,
 - if process A maps ANON, swap I/O should be charged to process B.
 - if process A maps FILE, I/O should be charged to process A.
maybe. 


Anyway, there will be ineraction with dirty_ratio of memcg (not implemeted yet)
and _Owner should be charged_ issue will be handled in this dirty_ratio layer.
More consideration is necessary, I think.


Bye,
-Kame


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