ia64/linux-2.6.18-xen.hg

view arch/mips/lib-32/watch.S @ 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
children
line source
1 /*
2 * This file is subject to the terms and conditions of the GNU General Public
3 * License. See the file "COPYING" in the main directory of this archive
4 * for more details.
5 *
6 * Kernel debug stuff to use the Watch registers.
7 * Useful to find stack overflows, dangling pointers etc.
8 *
9 * Copyright (C) 1995, 1996, 1999 by Ralf Baechle
10 */
11 #include <asm/asm.h>
12 #include <asm/mipsregs.h>
13 #include <asm/regdef.h>
15 .set noreorder
16 /*
17 * Parameter: a0 - logic address to watch
18 * Currently only KSEG0 addresses are allowed!
19 * a1 - set bit #1 to trap on load references
20 * bit #0 to trap on store references
21 * Results : none
22 */
23 LEAF(__watch_set)
24 li t0, 0x80000000
25 subu a0, t0
26 ori a0, 7
27 xori a0, 7
28 or a0, a1
29 mtc0 a0, CP0_WATCHLO
30 sw a0, watch_savelo
32 jr ra
33 mtc0 zero, CP0_WATCHHI
34 END(__watch_set)
36 /*
37 * Parameter: none
38 * Results : none
39 */
40 LEAF(__watch_clear)
41 jr ra
42 mtc0 zero, CP0_WATCHLO
43 END(__watch_clear)
45 /*
46 * Parameter: none
47 * Results : none
48 */
49 LEAF(__watch_reenable)
50 lw t0, watch_savelo
51 jr ra
52 mtc0 t0, CP0_WATCHLO
53 END(__watch_reenable)
55 /*
56 * Saved value of the c0_watchlo register for watch_reenable()
57 */
58 .data
59 watch_savelo: .word 0
60 .text