[Xen-devel] [PATCH 05 of 23] libxl: drop 8M slack for PV guests

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

# HG changeset patch
# User Ian Campbell <ian.campbell@xxxxxxxxxx>
# Date 1329148132 0
# Node ID 192eefb9e00e048333b01ee732a1b07071b90e7e
# Parent  d50d692ae52bca2d409415245e2fcd909259461a
libxl: drop 8M slack for PV guests.

As far as I can tell this serves no purpose. I think it relates to the old
8M to "account for backend allocations" which we used to add. This leaves a bit
of unpopulated space in the Pseudo-physical address space which can be used by
backends when mapping foreign memory. However 8M is not representative of that
any more and modern kernels do not operate in this way anyway.

I suspect an argument could be made for removing this from the libxl API
altogether but instead lets just set the overhead to 0.

Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

diff -r d50d692ae52b -r 192eefb9e00e tools/libxl/libxl_create.c
--- a/tools/libxl/libxl_create.c        Mon Feb 13 15:48:52 2012 +0000
+++ b/tools/libxl/libxl_create.c        Mon Feb 13 15:48:52 2012 +0000
@@ -107,7 +107,7 @@ void libxl_domain_build_info_init(libxl_
         b_info->u.hvm.xen_platform_pci = 1;
         break;
     case LIBXL_DOMAIN_TYPE_PV:
-        b_info->u.pv.slack_memkb = 8 * 1024;
+        b_info->u.pv.slack_memkb = 0;
         break;
     default:
         abort();

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