view lib/debug_locks.c @ 897:329ea0ccb344

balloon: try harder to balloon up under memory pressure.

Currently if the balloon driver is unable to increase the guest's
reservation it assumes the failure was due to reaching its full
allocation, gives up on the ballooning operation and records the limit
it reached as the "hard limit". The driver will not try again until
the target is set again (even to the same value).

However it is possible that ballooning has in fact failed due to
memory pressure in the host and therefore it is desirable to keep
attempting to reach the target in case memory becomes available. The
most likely scenario is that some guests are ballooning down while
others are ballooning up and therefore there is temporary memory
pressure while things stabilise. You would not expect a well behaved
toolstack to ask a domain to balloon to more than its allocation nor
would you expect it to deliberately over-commit memory by setting
balloon targets which exceed the total host memory.

This patch drops the concept of a hard limit and causes the balloon
driver to retry increasing the reservation on a timer in the same
manner as when decreasing the reservation.

Also if we partially succeed in increasing the reservation
(i.e. receive less pages than we asked for) then we may as well keep
those pages rather than returning them to Xen.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
author Keir Fraser <keir.fraser@citrix.com>
date Fri Jun 05 14:01:20 2009 +0100 (2009-06-05)
parents 831230e53067
line source
1 /*
2 * lib/debug_locks.c
3 *
4 * Generic place for common debugging facilities for various locks:
5 * spinlocks, rwlocks, mutexes and rwsems.
6 *
7 * Started by Ingo Molnar:
8 *
9 * Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
10 */
11 #include <linux/rwsem.h>
12 #include <linux/mutex.h>
13 #include <linux/module.h>
14 #include <linux/spinlock.h>
15 #include <linux/debug_locks.h>
17 /*
18 * We want to turn all lock-debugging facilities on/off at once,
19 * via a global flag. The reason is that once a single bug has been
20 * detected and reported, there might be cascade of followup bugs
21 * that would just muddy the log. So we report the first one and
22 * shut up after that.
23 */
24 int debug_locks = 1;
26 /*
27 * The locking-testsuite uses <debug_locks_silent> to get a
28 * 'silent failure': nothing is printed to the console when
29 * a locking bug is detected.
30 */
31 int debug_locks_silent;
33 /*
34 * Generic 'turn off all lock debugging' function:
35 */
36 int debug_locks_off(void)
37 {
38 if (xchg(&debug_locks, 0)) {
39 if (!debug_locks_silent) {
40 console_verbose();
41 return 1;
42 }
43 }
44 return 0;
45 }