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Message-ID: <1250041003.152221253087777235.JavaMail.root@zmail06.collab.prod.int.phx2.redhat.com>
Date: Wed, 16 Sep 2009 03:56:17 -0400 (EDT)
From: Miroslav Rezanina <mrezanin@...hat.com>
To: Jeremy Fitzhardinge <jeremy@...p.org>
Cc: linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.com
Subject: Re: [PATCH][v2.6.29][XEN] Return unused memory to hypervisor
> From: "Jeremy Fitzhardinge" <jeremy@...p.org>
> To: "Miroslav Rezanina" <mrezanin@...hat.com>
> Cc: linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.com
> Sent: Friday, September 4, 2009 1:26:24 AM GMT +01:00 Amsterdam / Berlin / Bern / Rome / Stockholm / Vienna
> Subject: Re: [PATCH][v2.6.29][XEN] Return unused memory to hypervisor
>
> On 08/19/09 06:05, Miroslav Rezanina wrote:
> > when running linux as XEN guest and use boot parameter mem= to set
> memory lower then is assigned to guest, not used memory should be
> returned to hypervisor as free. This is working with kernel available
> on xen.org pages, but is not working with kernel 2.6.29. Comparing
> both kernels I found code for returning unused memory to hypervisor is
> missing. Following patch add this functionality to 2.6.29 kernel.
> >
>
> Are you planning on submitting a revised patch along the lines I
> suggested?
>
> Thanks,
> J
General version of patch. This version checks the e820 map for holes
and returns all memory that is not mapped.
Patch:
===========
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index b58e963..acc9166 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -31,6 +31,7 @@
#include <xen/interface/version.h>
#include <xen/interface/physdev.h>
#include <xen/interface/vcpu.h>
+#include <xen/interface/memory.h>
#include <xen/features.h>
#include <xen/page.h>
#include <xen/hvc-console.h>
@@ -122,6 +123,59 @@ static int have_vcpu_info_placement =
#endif
;
+void __init xen_return_unused_memory(void)
+{
+ static struct e820map holes = {
+ .nr_map = 0
+ };
+ struct xen_memory_reservation reservation = {
+ .address_bits = 0,
+ .extent_order = 0,
+ .domid = DOMID_SELF
+ };
+ unsigned long last_end = 0;
+ int i;
+
+ for(i=0;i<e820.nr_map;i++) {
+ if (e820.map[i].addr > last_end) {
+ holes.map[holes.nr_map].addr = last_end;
+ holes.map[holes.nr_map].size =
+ e820.map[i].addr - last_end;
+ holes.nr_map++;
+ }
+ last_end = e820.map[i].addr + e820.map[i].size;
+ }
+
+ if (last_end < PFN_PHYS((u64)xen_start_info->nr_pages)) {
+ holes.map[holes.nr_map].addr=last_end;
+ holes.map[holes.nr_map].size =
+ PFN_PHYS((u64)xen_start_info->nr_pages) - last_end;
+ holes.nr_map++;
+ }
+
+ if (holes.nr_map == 0)
+ return;
+
+ for(i=0;i<holes.nr_map;i++) {
+ unsigned long spfn = holes.map[i].addr >> PAGE_SHIFT;
+ unsigned long epfn = ((holes.map[i].addr + holes.map[i].size) >> PAGE_SHIFT);
+ int ret;
+
+ if (spfn % PAGE_SIZE != 0)
+ spfn++;
+
+ if (spfn >= epfn)
+ continue;
+
+ set_xen_guest_handle(reservation.extent_start,
+ ((unsigned long *)xen_start_info->mfn_list) + spfn);
+
+ reservation.nr_extents = epfn - spfn;
+ ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation,
+ &reservation);
+ BUG_ON (ret != epfn - spfn);
+ }
+}
static void xen_vcpu_setup(int cpu)
{
@@ -1057,6 +1111,8 @@ static __init void xen_post_allocator_init(void)
SetPagePinned(virt_to_page(level3_user_vsyscall));
#endif
xen_mark_init_mm_pinned();
+
+/* xen_return_unused_memory(); */
}
/* This is called once we have the cpu_possible_map */
--
Miroslav Rezanina
Software Engineer - Virtualization Team - XEN kernel
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