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From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] [PATCH 4/4] Reallocate dma buffers in read/write
	path if needed
Date: Sun, 5 Oct 2008 00:00:27 +0100
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To: Ryan Harper <ryanh@us.ibm.com>
Cc: qemu-devel@nongnu.org, Anthony Liguori <aliguori@us.ibm.com>, aliguori@linux.ibm.com, kvm@vger.kernel.org, Avi Kivity <avi@redhat.com>

On Saturday 04 October 2008, Ryan Harper wrote:
> In all, it seems silly to worry about this sort of thing since the
> entire process could be contained with process ulimits if this is really
> a concern. =A0Are we any more concerned that by splitting the requests
> into many smaller requests that we're wasting cpu, pegging the
> processor to 100% in some cases?

Using small requests may be a bit inefficient, but it still works and allow=
s=20
the guest to make progress.

Allocating very large quantities of memory is very likely to kill the VM on=
e=20
way or another. This is not acceptable, especially when the guest hasn't ev=
en=20
done anything wrong. There are legitimate circumstances where the size of t=
he=20
outstanding IO requests may be comparable to the guest ram size.

Paul