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Date:	Sun, 30 Sep 2012 11:52:05 -0700
From:	"H. Peter Anvin" <>
To:	Pierre Beck <>
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...

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

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