linux-kernel - Re: [PATCH 7/8] writeback: sync old inodes first in background writeback

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Message-ID: <20100725120345.GA1817@barrios-desktop>
Date:	Sun, 25 Jul 2010 21:03:45 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Mel Gorman <mel@....ul.ie>, Wu Fengguang <fengguang.wu@...el.com>,
	Christoph Hellwig <hch@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Dave Chinner <david@...morbit.com>,
	Chris Mason <chris.mason@...cle.com>,
	Nick Piggin <npiggin@...e.de>, Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [PATCH 7/8] writeback: sync old inodes first in background
 writeback

On Sun, Jul 25, 2010 at 07:43:20PM +0900, KOSAKI Motohiro wrote:
> Hi
> 
> sorry for the delay.
> 
> > Will you be picking it up or should I? The changelog should be more or less
> > the same as yours and consider it
> > 
> > Signed-off-by: Mel Gorman <mel@....ul.ie>
> > 
> > It'd be nice if the original tester is still knocking around and willing
> > to confirm the patch resolves his/her problem. I am running this patch on
> > my desktop at the moment and it does feel a little smoother but it might be
> > my imagination. I had trouble with odd stalls that I never pinned down and
> > was attributing to the machine being commonly heavily loaded but I haven't
> > noticed them today.
> > 
> > It also needs an Acked-by or Reviewed-by from Kosaki Motohiro as it alters
> > logic he introduced in commit [78dc583: vmscan: low order lumpy reclaim also
> > should use PAGEOUT_IO_SYNC]
> 
> My reviewing doesn't found any bug. however I think original thread have too many guess
> and we need to know reproduce way and confirm it.
> 
> At least, we need three confirms.
>  o original issue is still there?
>  o DEF_PRIORITY/3 is best value?

I agree. Wu, how do you determine DEF_PRIORITY/3 of LRU?
I guess system has 512M and 22M writeback pages. 
So you may determine it for skipping max 32M writeback pages.
Is right?

And I have a question of your below comment. 

"As the default dirty throttle ratio is 20%, sync write&wait
will hardly be triggered by pure dirty pages"

I am not sure exactly what you mean but at least DEF_PRIOIRTY/3 seems to be
related to dirty_ratio. It always can be changed by admin.
Then do we have to determine magic value(DEF_PRIORITY/3)  proportional to dirty_ratio?

-- 
Kind regards,
Minchan Kim
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