linux-kernel - Re: [PATCH] writeback: remove the internal 5% low bound on dirty

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Message-Id: <201008201550.54164.kernel@kolivas.org>
Date:	Fri, 20 Aug 2010 15:50:54 +1000
From:	Con Kolivas <kernel@...ivas.org>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Wu Fengguang <fengguang.wu@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, riel@...hat.com, david@...morbit.com,
	hch@....de, axboe@...nel.dk
Subject: Re: [PATCH] writeback: remove the internal 5% low bound on dirty_ratio

On Fri, 20 Aug 2010 02:13:25 pm KOSAKI Motohiro wrote:
> > The dirty_ratio was silently limited to >= 5%. This is not a user
> > expected behavior. Let's rip it.
> >
> > It's not likely the user space will depend on the old behavior.
> > So the risk of breaking user space is very low.
> >
> > CC: Jan Kara <jack@...e.cz>
> > CC: Neil Brown <neilb@...e.de>
> > Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
>
> Thank you.
> 	Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>

I have tried to do this in the past, and setting this value to 0 on some 
machines caused the machine to come to a complete standstill with small 
writes to disk. It seemed there was some kind of "minimum" amount of data 
required by the VM before anything would make it to the disk and I never 
quite found out where that blockade occurred. This was some time ago (3 years 
ago) so I'm not sure if the problem has since been fixed in the VM since 
then. I suggest you do some testing with this value set to zero before 
approving this change.

Regards,
--
-ck
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