ia64/linux-2.6.18-xen.hg

view arch/sparc/prom/devops.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
children
line source
1 /* $Id: devops.c,v 1.13 2000/08/26 02:38:03 anton Exp $
2 * devops.c: Device operations using the PROM.
3 *
4 * Copyright (C) 1995 David S. Miller (davem@caip.rutgers.edu)
5 */
6 #include <linux/types.h>
7 #include <linux/kernel.h>
8 #include <linux/sched.h>
10 #include <asm/openprom.h>
11 #include <asm/oplib.h>
13 extern void restore_current(void);
15 /* Open the device described by the string 'dstr'. Returns the handle
16 * to that device used for subsequent operations on that device.
17 * Returns -1 on failure.
18 */
19 int
20 prom_devopen(char *dstr)
21 {
22 int handle;
23 unsigned long flags;
24 spin_lock_irqsave(&prom_lock, flags);
25 switch(prom_vers) {
26 case PROM_V0:
27 handle = (*(romvec->pv_v0devops.v0_devopen))(dstr);
28 if(handle == 0) handle = -1;
29 break;
30 case PROM_V2:
31 case PROM_V3:
32 handle = (*(romvec->pv_v2devops.v2_dev_open))(dstr);
33 break;
34 default:
35 handle = -1;
36 break;
37 };
38 restore_current();
39 spin_unlock_irqrestore(&prom_lock, flags);
41 return handle;
42 }
44 /* Close the device described by device handle 'dhandle'. */
45 int
46 prom_devclose(int dhandle)
47 {
48 unsigned long flags;
49 spin_lock_irqsave(&prom_lock, flags);
50 switch(prom_vers) {
51 case PROM_V0:
52 (*(romvec->pv_v0devops.v0_devclose))(dhandle);
53 break;
54 case PROM_V2:
55 case PROM_V3:
56 (*(romvec->pv_v2devops.v2_dev_close))(dhandle);
57 break;
58 default:
59 break;
60 };
61 restore_current();
62 spin_unlock_irqrestore(&prom_lock, flags);
63 return 0;
64 }
66 /* Seek to specified location described by 'seekhi' and 'seeklo'
67 * for device 'dhandle'.
68 */
69 void
70 prom_seek(int dhandle, unsigned int seekhi, unsigned int seeklo)
71 {
72 unsigned long flags;
73 spin_lock_irqsave(&prom_lock, flags);
74 switch(prom_vers) {
75 case PROM_V0:
76 (*(romvec->pv_v0devops.v0_seekdev))(dhandle, seekhi, seeklo);
77 break;
78 case PROM_V2:
79 case PROM_V3:
80 (*(romvec->pv_v2devops.v2_dev_seek))(dhandle, seekhi, seeklo);
81 break;
82 default:
83 break;
84 };
85 restore_current();
86 spin_unlock_irqrestore(&prom_lock, flags);
88 return;
89 }