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From: Pekka Enberg <penberg@cs.helsinki.fi>
To: Sasha Levin <levinsasha928@gmail.com>
Cc: mingo@elte.hu, asias.hejun@gmail.com, prasadjoshi124@gmail.com,
	avi@redhat.com, gorcunov@gmail.com, kvm@vger.kernel.org
Subject: Re: [PATCH 1/2] kvm tools: Add memory gap for larger RAM sizes
Date: Wed, 11 May 2011 09:26:08 +0300	[thread overview]
Message-ID: <4DCA2C00.9090907@cs.helsinki.fi> (raw)
In-Reply-To: <1305094876.2249.2.camel@sasha>

On 5/11/11 9:21 AM, Sasha Levin wrote:
> If you feel the 512MB vs guest_flat_to_host() trade-off is worth it,
> I'll change it to work that way.

Why would it not be? This is 64-bit only, right? There's plenty of 
virtual address
space and mprotect() should make sure we never allocate physical pages 
for it.
Sure, there's some in-kernel overhead involved as well, but that's 
extremely small.

I'm not worried about performance in guest_flat_to_host() but I think 
the current
implementation is not very clean. If you want to mmap() two separate 
regions,
we should have our own internal "memory map" that's used for this (and for
populating KVM end E820 maps).

So I think mmap'ing the gap is the cleanest solution for now. We can 
revisit the
decision if we need even more regions in the future.

                     Pekka

  reply	other threads:[~2011-05-11 16:56 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-05-10 21:05 [PATCH 1/2] kvm tools: Add memory gap for larger RAM sizes Sasha Levin
2011-05-10 21:05 ` [PATCH 2/2] kvm tools: Prevent PFN wraparound Sasha Levin
2011-05-10 21:09   ` Pekka Enberg
2011-05-11  5:37 ` [PATCH 1/2] kvm tools: Add memory gap for larger RAM sizes Pekka Enberg
2011-05-11  6:21   ` Sasha Levin
2011-05-11  6:26     ` Pekka Enberg [this message]
2011-05-11  7:10       ` Ingo Molnar
2011-05-11  8:30   ` Avi Kivity
2011-05-11  8:44     ` Ingo Molnar
2011-05-11  9:06       ` Avi Kivity
2011-05-11  9:28         ` Pekka Enberg

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