linux-kernel - Re: [PATCH][RFC] dirty balancing for cgroups

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Date:	Wed,  6 Aug 2008 18:10:05 +0900 (JST)
From:	yamamoto@...inux.co.jp (YAMAMOTO Takashi)
To:	kamezawa.hiroyu@...fujitsu.com
Cc:	linux-mm@...ck.org, menage@...gle.com,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, a.p.zijlstra@...llo.nl
Subject: Re: [PATCH][RFC] dirty balancing for cgroups

hi,

> On Wed,  6 Aug 2008 17:20:46 +0900 (JST)
> yamamoto@...inux.co.jp (YAMAMOTO Takashi) wrote:
> 
> > hi,
> > 
> > > On Fri, 11 Jul 2008 17:34:46 +0900 (JST)
> > > yamamoto@...inux.co.jp (YAMAMOTO Takashi) wrote:
> > > 
> > > > hi,
> > > > 
> > > > > > my patch penalizes heavy-writer cgroups as task_dirty_limit does
> > > > > > for heavy-writer tasks.  i don't think that it's necessary to be
> > > > > > tied to the memory subsystem because i merely want to group writers.
> > > > > > 
> > > > > Hmm, maybe what I need is different from this ;)
> > > > > Does not seem to be a help for memory reclaim under memcg.
> > > > 
> > > > to implement what you need, i think that we need to keep track of
> > > > the numbers of dirty-pages in each memory cgroups as a first step.
> > > > do you agree?
> > > > 
> > > yes, I think so, now.
> > > 
> > > may be not difficult but will add extra overhead ;( Sigh..
> > 
> > the following is a patch to add the overhead. :)
> > any comments?
> > 
> Do you have some numbers ? ;) 

not yet.

> I like this because this seems very straightforward. thank you.

good to hear.

> How about changing these to be
> 
> ==
> void mem_cgroup_test_set_page_dirty()
> {
> 	if (try_lock_page_cgroup(pg)) {
> 		pc = page_get_page_cgroup(pg);
> 		if (pc ......) {
> 		}
> 		unlock_page_cgroup(pg)
> 	}
> }
> ==

i'm not sure how many opportunities to update statistics
we would lose for the trylock failure.
although the statistics don't need to be too precise,
its error should have a reasonable upper-limit to be useful.

> Off-topic: I wonder we can delete this "lock" in future.
> 
> Because page->page_cgroup is
>  1. attached at first use.(Obiously no race with set_dirty)
>  2. deleted at removal. (force_empty is problematic here..)

i hope it's possible. :)

YAMAMOTO Takashi

> 
> But, now, we need this lock.
> 
> Thanks,
> -Kame
> 
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