Re: Memory management woes - order 1 allocation failures

From: Mel Gorman
Date: Tue Mar 02 2010 - 14:11:33 EST

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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