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Subject[PATCH 6/7] xen/setup: Make dom0_mem=XGB behavior be similar to classic Xen kernels.
Date
Meaning that we will allocate up to XGB and not consider the
rest of the memory as a possible balloon goal.

This results in /proc/meminfo reporting:

-MemTotal: 2845024 kB
-MemFree: 2497716 kB
+MemTotal: 2927192 kB
+MemFree: 2458952 kB
...
-DirectMap4k: 8304640 kB
+DirectMap4k: 3063808 kB
DirectMap2M: 0 kB

on a 8GB machine with 'dom0_mem=3GB' on the Xen hypervisor line.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
arch/x86/xen/setup.c | 16 ++++++++++++++++
1 files changed, 16 insertions(+), 0 deletions(-)

diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index 2a12143..4e4aa8e 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -261,11 +261,27 @@ static unsigned long __init xen_get_max_pages(void)
* the current maximum rather than the static maximum. In this
* case the e820 map provided to us will cover the static
* maximum region.
+ *
+ * The dom0_mem=min:X,max:Y tweaks options differently depending
+ * on the version, but in general this is what we get:
+ * | XENMEM_maximum_reser | nr_pages
+ * --------------++-----------------------+-------------------
+ * no dom0_mem | INT_MAX | the max_phys_pfn
+ * =3G | INT_MAX | 786432
+ * =max:3G | 786432 | 786432
+ * =min:1G,max:3G| 262144 | 786432
+ *
+ * The =3G is often used and it lead to us initially setting
+ * 786432 and allowing dom0 to balloon up to the max_physical_pfn.
+ * This is at odd with the classic XenOClassic so lets emulate
+ * the classic behavior.
*/
if (xen_initial_domain()) {
ret = HYPERVISOR_memory_op(XENMEM_maximum_reservation, &domid);
if (ret > 0)
max_pages = ret;
+ if (ret == -1UL)
+ max_pages = xen_start_info->nr_pages;
}

return min(max_pages, MAX_DOMAIN_PAGES);
--
1.7.7.5


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