ia64/linux-2.6.18-xen.hg

view drivers/md/dm-path-selector.h @ 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 * Copyright (C) 2003 Sistina Software.
3 * Copyright (C) 2004 Red Hat, Inc. All rights reserved.
4 *
5 * Module Author: Heinz Mauelshagen
6 *
7 * This file is released under the GPL.
8 *
9 * Path-Selector registration.
10 */
12 #ifndef DM_PATH_SELECTOR_H
13 #define DM_PATH_SELECTOR_H
15 #include <linux/device-mapper.h>
17 #include "dm-mpath.h"
19 /*
20 * We provide an abstraction for the code that chooses which path
21 * to send some io down.
22 */
23 struct path_selector_type;
24 struct path_selector {
25 struct path_selector_type *type;
26 void *context;
27 };
29 /* Information about a path selector type */
30 struct path_selector_type {
31 char *name;
32 struct module *module;
34 unsigned int table_args;
35 unsigned int info_args;
37 /*
38 * Constructs a path selector object, takes custom arguments
39 */
40 int (*create) (struct path_selector *ps, unsigned argc, char **argv);
41 void (*destroy) (struct path_selector *ps);
43 /*
44 * Add an opaque path object, along with some selector specific
45 * path args (eg, path priority).
46 */
47 int (*add_path) (struct path_selector *ps, struct path *path,
48 int argc, char **argv, char **error);
50 /*
51 * Chooses a path for this io, if no paths are available then
52 * NULL will be returned.
53 *
54 * repeat_count is the number of times to use the path before
55 * calling the function again. 0 means don't call it again unless
56 * the path fails.
57 */
58 struct path *(*select_path) (struct path_selector *ps,
59 unsigned *repeat_count);
61 /*
62 * Notify the selector that a path has failed.
63 */
64 void (*fail_path) (struct path_selector *ps, struct path *p);
66 /*
67 * Ask selector to reinstate a path.
68 */
69 int (*reinstate_path) (struct path_selector *ps, struct path *p);
71 /*
72 * Table content based on parameters added in ps_add_path_fn
73 * or path selector status
74 */
75 int (*status) (struct path_selector *ps, struct path *path,
76 status_type_t type, char *result, unsigned int maxlen);
78 int (*end_io) (struct path_selector *ps, struct path *path);
79 };
81 /* Register a path selector */
82 int dm_register_path_selector(struct path_selector_type *type);
84 /* Unregister a path selector */
85 int dm_unregister_path_selector(struct path_selector_type *type);
87 /* Returns a registered path selector type */
88 struct path_selector_type *dm_get_path_selector(const char *name);
90 /* Releases a path selector */
91 void dm_put_path_selector(struct path_selector_type *pst);
93 #endif