linux-kernel - Re: 3.6-rc7 32-bit PAE miscalculates dirty page limits

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Message-ID: <506894D5.5060101@zytor.com>
Date:	Sun, 30 Sep 2012 11:52:05 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Pierre Beck <mail@...rre-beck.de>
CC:	linux-kernel@...r.kernel.org
Subject: Re: 3.6-rc7 32-bit PAE miscalculates dirty page limits

On 09/30/2012 02:38 AM, Pierre Beck wrote:
> Hi,
>
> there seems to be a bug in either ext4 or VM code triggered with 16 GB
> memory when compiled with 32-bit and PAE. dirty_background_ratio
> defaults to 10, dirty_ratio to 20. But in effect, dirty pages are
> strongly limited (zero or negative?). I observed extreme I/O wait states
> and slow disk access. A quick cure was to set dirty_bytes and
> dirty_background_bytes to sane values, overriding the ratios. An
> educated guess: the result of dirty_ratio calculation is stored as an
> unsigned 32-bit integer and overflows?
>

Seriously, why are you running a 32-bit kernel on memory sizes this 
large?  Yes, in theory it should work up to 64 GB but claims are that 
the kernel doesn't even boot if you try...

	-hpa
-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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