[Xen-changelog] [linux-2.6.18-xen] linux/balloon: don't allow ballooning down a domain below a reasonable limit

["Xen patchbot-linux-2.6.18-xen" <patchbot-linux-2.6.18-xen@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1207431409 -3600
# Node ID b61443b1bf7690f421dbdfbcd62cf83497deb4a0
# Parent  0d6c9c975eaee85e35d4007b1b84cafbfbb24378
linux/balloon: don't allow ballooning down a domain below a reasonable limit

Reasonable is hard to judge; we don't want to disallow small domains.
But the system needs a reasonable amount of memory to perform its
duties, set up tables, etc. If on the other hand, the admin is able
to set up and boot up correctly a very small domain, there's no point
in forcing it to be larger. We end up with some kind of logarithmic
function, approximated.

Signed-off-by: Kurt Garloff <garloff@xxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>
---
 drivers/xen/balloon/balloon.c |   37 ++++++++++++++++++++++++++++++++++++-
 1 files changed, 36 insertions(+), 1 deletion(-)

diff -r 0d6c9c975eae -r b61443b1bf76 drivers/xen/balloon/balloon.c
--- a/drivers/xen/balloon/balloon.c     Fri Apr 04 13:27:48 2008 +0100
+++ b/drivers/xen/balloon/balloon.c     Sat Apr 05 22:36:49 2008 +0100
@@ -194,6 +194,41 @@ static unsigned long current_target(void
        return target;
 }
 
+static unsigned long minimum_target(void)
+{
+#ifndef CONFIG_XEN
+       return 0;
+#else
+       unsigned long min_pages, curr_pages = current_target();
+
+#define MB2PAGES(mb) ((mb) << (20 - PAGE_SHIFT))
+       /* Simple continuous piecewiese linear function:
+        *  max MiB -> min MiB  gradient
+        *       0         0
+        *      16        16
+        *      32        24
+        *     128        72    (1/2)
+        *     512       168    (1/4)
+        *    2048       360    (1/8)
+        *    8192       552    (1/32)
+        *   32768      1320
+        *  131072      4392
+        */
+       if (max_pfn < MB2PAGES(128))
+               min_pages = MB2PAGES(8) + (max_pfn >> 1);
+       else if (max_pfn < MB2PAGES(512))
+               min_pages = MB2PAGES(40) + (max_pfn >> 2);
+       else if (max_pfn < MB2PAGES(2048))
+               min_pages = MB2PAGES(104) + (max_pfn >> 3);
+       else
+               min_pages = MB2PAGES(296) + (max_pfn >> 5);
+#undef MB2PAGES
+
+       /* Don't enforce growth */
+       return min(min_pages, curr_pages);
+#endif
+}
+
 static int increase_reservation(unsigned long nr_pages)
 {
        unsigned long  pfn, i, flags;
@@ -384,7 +419,7 @@ void balloon_set_new_target(unsigned lon
 {
        /* No need for lock. Not read-modify-write updates. */
        bs.hard_limit   = ~0UL;
-       bs.target_pages = target;
+       bs.target_pages = max(target, minimum_target());
        schedule_work(&balloon_worker);
 }
 

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