WARNING - OLD ARCHIVES

This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
   
 
 
Xen 
 
Home Products Support Community News
 
   
 

xen-devel

[Xen-devel] [PATCH 1/7] xen: use maximum reservation to limit amount of

To: xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-devel] [PATCH 1/7] xen: use maximum reservation to limit amount of usable RAM
From: David Vrabel <david.vrabel@xxxxxxxxxx>
Date: Thu, 15 Sep 2011 13:29:22 +0100
Cc: David Vrabel <david.vrabel@xxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Delivery-date: Thu, 15 Sep 2011 05:31:31 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <1316089768-22461-1-git-send-email-david.vrabel@xxxxxxxxxx>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
References: <1316089768-22461-1-git-send-email-david.vrabel@xxxxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
From: David Vrabel <david.vrabel@xxxxxxxxxx>

Use the domain's maximum reservation to limit the amount of extra RAM
for the memory balloon. This reduces the size of the pages tables and
the amount of reserved low memory (which defaults to about 1/32 of the
total RAM).

On a system with 8 GiB of RAM with the domain limited to 1 GiB the
kernel reports:

Before:

Memory: 627792k/4472000k available

After:

Memory: 549740k/11132224k available

A increase of about 76 MiB (~1.5% of the unused 7 GiB).  The reserved
low memory is also reduced from 253 MiB to 32 MiB.  The total
additional usable RAM is 329 MiB.

For dom0, this requires at patch to Xen ('x86: use 'dom0_mem' to limit
the number of pages for dom0')[1].

[1] http://lists.xensource.com/archives/html/xen-devel/2011-08/msg00567.html

Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
---
 arch/x86/xen/setup.c |   19 +++++++++++++++++++
 1 files changed, 19 insertions(+), 0 deletions(-)

diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index df118a8..c3b8d44 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -184,6 +184,19 @@ static unsigned long __init xen_set_identity(const struct 
e820entry *list,
                                        PFN_UP(start_pci), PFN_DOWN(last));
        return identity;
 }
+
+static unsigned long __init xen_get_max_pages(void)
+{
+       unsigned long max_pages = MAX_DOMAIN_PAGES;
+       domid_t domid = DOMID_SELF;
+       int ret;
+
+       ret = HYPERVISOR_memory_op(XENMEM_maximum_reservation, &domid);
+       if (ret > 0)
+               max_pages = ret;
+       return min(max_pages, MAX_DOMAIN_PAGES);
+}
+
 /**
  * machine_specific_memory_setup - Hook for machine specific memory setup.
  **/
@@ -292,6 +305,12 @@ char * __init xen_memory_setup(void)
 
        sanitize_e820_map(e820.map, ARRAY_SIZE(e820.map), &e820.nr_map);
 
+       extra_limit = xen_get_max_pages();
+       if (extra_limit >= max_pfn)
+               extra_pages = extra_limit - max_pfn;
+       else
+               extra_pages = 0;
+
        extra_pages += xen_return_unused_memory(xen_start_info->nr_pages, 
&e820);
 
        /*
-- 
1.7.2.5


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel