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Re: [Qemu-devel] [PATCH] Allocate translation buffer before guest RAM, i


From: Anthony Liguori
Subject: Re: [Qemu-devel] [PATCH] Allocate translation buffer before guest RAM, in case guest RAM is too large on 64 bit hosts
Date: Wed, 22 Oct 2008 10:12:57 -0500
User-agent: Thunderbird 2.0.0.17 (X11/20080925)

Juergen Lock wrote:
In article <address@hidden> you write:
Juergen Lock wrote:
Hi!

 The following patch appears to fix -m >= 1024 on recent FreeBSD/amd64 hosts
(RELENG_7/HEAD) that no longer return high addresses for allocations by
default (which was the original reason for r5331.)  As this makes sense
in any case when you pass something like -m 4096 on hosts that allocate
from low addresses by default (there would be no room left for the
translation buffer in the low vm where it needs to be), I patched it like
this instead of conditionalizing the mmap hack from r5331 on the FreeBSD
version.
I fear there is too much magic here.

Heh.

Does FreeBSD not have a flag to mmap from high memory?

 I don't think so.

 What is the the original problem?

 code_gen_buffer needs to be in the lower 4G (because of branches with
32 bit offsets etc.)

Can you resubmit the patch with a big comment explaining why the allocation order is important?

Regards,

Anthony Liguori

Regards,

Anthony Liguori

 Thanx,
        Juergen





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