linux-kernel - Re: 2.6.36 io bring the system to its knees

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Date:	Tue, 2 Nov 2010 09:20:06 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Dimitrios Apostolou <jimis@....net>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: 2.6.36 io bring the system to its knees

On Mon, Nov 01, 2010 at 01:09:34AM +0000, Dimitrios Apostolou wrote:
> Hello, 
> 
> On Sun, 31 Oct 2010 09:51:32 +0800, Wu Fengguang wrote:
> > It may also help to lower the dirty ratio.
> > 
> > echo 5 > /proc/sys/vm/dirty_ratio
> > 
> > Memory pressure + heavy write can easily hurt responsiveness.
> > 
> > - eats up to 20% (the default value for dirty_ratio) memory with dirty
> >   pages and hence increase the memory pressure and number of swap IO
> 
> My experience has been different with that. Wouldn't it make more sense 
> to _increase_ dirty_ratio (to 50 lets say) and at the same time decrease 
> dirty_background_ratio? That way writing to disk starts early, but the 
> related apps stall waiting for I/O only when dirty_ratio is reached.

50% dirty ratio may help before the system goes thrashing (writing
processes will be throttled less/later). However Aidar is seeing hours
of unresponsiveness with heavy IO, in this case large dirty ratio
won't help reduce the throttling any more.

Thanks,
Fengguang
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