xen: use maximum reservation to limit amount of usable RAM
commit d312ae878b6aed3912e1acaaf5d0b2a9d08a4f11 upstream.
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') (c/s 23790)
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index 60aeeb5..d78cd40 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -185,6 +185,19 @@
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.
**/
@@ -293,6 +306,12 @@
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);
/*