linux-kernel - Re: [patch 0/7] cpuset writeback throttling

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Message-Id: <20081105133157.db8bae72.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Wed, 5 Nov 2008 13:31:57 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Christoph Lameter <cl@...ux-foundation.org>, peterz@...radead.org,
	rientjes@...gle.com, npiggin@...e.de, menage@...gle.com,
	dfults@....com, linux-kernel@...r.kernel.org,
	containers@...ts.osdl.org, righi.andrea@...il.com
Subject: Re: [patch 0/7] cpuset writeback throttling

On Tue, 4 Nov 2008 19:05:05 -0800
Andrew Morton <akpm@...ux-foundation.org> wrote:
> Generally, I worry that this is a specific fix to a specific problem
> encountered on specific machines with specific setups and specific
> workloads, and that it's just all too low-level and myopic.
> 
> And now we're back in the usual position where there's existing code and
> everyone says it's terribly wonderful and everyone is reluctant to step
> back and look at the big picture.  Am I wrong?
> 
> 
> Plus: we need per-memcg dirty-memory throttling, and this is more
> important than per-cpuset, I suspect.  How will the (already rather
> buggy) code look once we've stuffed both of them in there?
> 
> 
IIUC, Andrea Righ posted 2 patches around dirty_ratio. (added him to CC:)
in early October.

  (1) patch for adding dirty_ratio_pcm. (1/100000)
  (2) per-memcg dirty ratio. (maybe this..http://lkml.org/lkml/2008/9/12/121)
 
(1) should be just posted again.

Because we have changed page_cgroup implementation, (2) should be reworked.
"rework" itself will not be very difficult.
(.... we tend to be stick to "what interface is the best" discussion ;) 

But memcg itself is not so weak against dirty_pages because we don't call
try_to_free_pages() becasue of memory shortage but because of memory limitation.

BTW, in my current stack, followings are queued.
   a. handle SwapCache in proper way in memcg.
   b. handle swap_cgroup (if configured)
   c. make LRU handling easier

For making per-memcg dirty_ratio sane, (a) should go ahead. I do (a) now.
If Andrea seems to be too busy, I'll schedule dirty_ratio-for-memcg as my work.

Thanks,
-Kame

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