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

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Date:	Fri, 24 Jul 2009 17:48:53 +0900 (JST)
From:	Ryo Tsuruta <ryov@...inux.co.jp>
To:	kamezawa.hiroyu@...fujitsu.com
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

KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> 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. 

I think that even process A maps ANON, it should be charged to process A
because the memory pressure is caused by process A. It seems natual
for me that a process which consumes more resources is more likely to
get penalty.

> 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.

I'll keep thinking how it should be done.

Thanks,
Ryo Tsuruta
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