linux-kernel - Re: Memory management woes - order 1 allocation failures

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Message-ID: <20100302191110.GB11355@csn.ul.ie>
Date:	Tue, 2 Mar 2010 19:11:10 +0000
From:	Mel Gorman <mel@....ul.ie>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Frans Pop <elendil@...net.nl>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: Memory management woes - order 1 allocation failures

On Tue, Mar 02, 2010 at 06:34:51PM +0000, Alan Cox wrote:
> > For reasons that are not particularly clear to me, tty_buffer_alloc() is
> > called far more frequently in 2.6.33 than in 2.6.24. I instrumented the
> > function to print out the size of the buffers allocated, booted under
> > qemu and would just "cat /bin/ls" to see what buffers were allocated.
> > 2.6.33 allocates loads, including high-order allocations. 2.6.24
> > appeared to allocate once and keep silent.
> 
> The pty layer is using them now and didn't before. That will massively
> distort your numhers.
> 

That makes perfect sense. It explains why only one allocation showed up
because it must belong to the tty attached to the serial console.

Thanks Alan.

> > While there have been snags recently with respect to high-order
> > allocation failures in recent kernels, this might be one of the cases
> > where it's due to subsystems requesting high-order allocations more.
> 
> The pty code certainly triggered more such allocations. I've sent Greg
> patches to make the tty buffering layer allocate sensible sizes as it
> doesn't need multiple page allocations in the first place.
> 

Greg, what's the story with these patches?

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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