view drivers/md/dm-bio-record.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
line source
1 /*
2 * Copyright (C) 2004-2005 Red Hat, Inc. All rights reserved.
3 *
4 * This file is released under the GPL.
5 */
7 #ifndef DM_BIO_RECORD_H
8 #define DM_BIO_RECORD_H
10 #include <linux/bio.h>
12 /*
13 * There are lots of mutable fields in the bio struct that get
14 * changed by the lower levels of the block layer. Some targets,
15 * such as multipath, may wish to resubmit a bio on error. The
16 * functions in this file help the target record and restore the
17 * original bio state.
18 */
19 struct dm_bio_details {
20 sector_t bi_sector;
21 struct block_device *bi_bdev;
22 unsigned int bi_size;
23 unsigned short bi_idx;
24 unsigned long bi_flags;
25 };
27 static inline void dm_bio_record(struct dm_bio_details *bd, struct bio *bio)
28 {
29 bd->bi_sector = bio->bi_sector;
30 bd->bi_bdev = bio->bi_bdev;
31 bd->bi_size = bio->bi_size;
32 bd->bi_idx = bio->bi_idx;
33 bd->bi_flags = bio->bi_flags;
34 }
36 static inline void dm_bio_restore(struct dm_bio_details *bd, struct bio *bio)
37 {
38 bio->bi_sector = bd->bi_sector;
39 bio->bi_bdev = bd->bi_bdev;
40 bio->bi_size = bd->bi_size;
41 bio->bi_idx = bd->bi_idx;
42 bio->bi_flags = bd->bi_flags;
43 }
45 #endif