[Xen-changelog] [xen-unstable] Allow max_pages to be set to less than tot_pages

[Xen patchbot-unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User Keir Fraser <keir@xxxxxxx>
# Date 1287922384 -3600
# Node ID 2208a036f8d9d932de8ab0aa0206f5c57dba8728
# Parent  c6e2f69e1807fb232b16983b040489fe30241cd7
Allow max_pages to be set to less than tot_pages

The memory allocation code sometimes needs to enforce that a guest
that's been told to balloon down isn't going to expand further
(because it's still executing a previous balloon-up operation).  That
means being able to set the desired max_pages even before the balloon
driver has brought tot_pages down to the right level.

Signed-off-by: Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Acked-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
---
 xen/common/domctl.c |   12 +++++++-----
 1 files changed, 7 insertions(+), 5 deletions(-)

diff -r c6e2f69e1807 -r 2208a036f8d9 xen/common/domctl.c
--- a/xen/common/domctl.c       Sun Oct 24 13:09:50 2010 +0100
+++ b/xen/common/domctl.c       Sun Oct 24 13:13:04 2010 +0100
@@ -770,11 +770,13 @@ long do_domctl(XEN_GUEST_HANDLE(xen_domc
         new_max = op->u.max_mem.max_memkb >> (PAGE_SHIFT-10);
 
         spin_lock(&d->page_alloc_lock);
-        if ( new_max >= d->tot_pages )
-        {
-            d->max_pages = new_max;
-            ret = 0;
-        }
+        /*
+         * NB. We removed a check that new_max >= current tot_pages; this means
+         * that the domain will now be allowed to "ratchet" down to new_max. In
+         * the meantime, while tot > max, all new allocations are disallowed.
+         */
+        d->max_pages = new_max;
+        ret = 0;
         spin_unlock(&d->page_alloc_lock);
 
     max_mem_out:

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