ia64/linux-2.6.18-xen.hg

view drivers/mtd/mtdblock_ro.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 /*
2 * $Id: mtdblock_ro.c,v 1.19 2004/11/16 18:28:59 dwmw2 Exp $
3 *
4 * (C) 2003 David Woodhouse <dwmw2@infradead.org>
5 *
6 * Simple read-only (writable only for RAM) mtdblock driver
7 */
9 #include <linux/init.h>
10 #include <linux/slab.h>
11 #include <linux/mtd/mtd.h>
12 #include <linux/mtd/blktrans.h>
14 static int mtdblock_readsect(struct mtd_blktrans_dev *dev,
15 unsigned long block, char *buf)
16 {
17 size_t retlen;
19 if (dev->mtd->read(dev->mtd, (block * 512), 512, &retlen, buf))
20 return 1;
21 return 0;
22 }
24 static int mtdblock_writesect(struct mtd_blktrans_dev *dev,
25 unsigned long block, char *buf)
26 {
27 size_t retlen;
29 if (dev->mtd->write(dev->mtd, (block * 512), 512, &retlen, buf))
30 return 1;
31 return 0;
32 }
34 static void mtdblock_add_mtd(struct mtd_blktrans_ops *tr, struct mtd_info *mtd)
35 {
36 struct mtd_blktrans_dev *dev = kmalloc(sizeof(*dev), GFP_KERNEL);
38 if (!dev)
39 return;
41 memset(dev, 0, sizeof(*dev));
43 dev->mtd = mtd;
44 dev->devnum = mtd->index;
45 dev->blksize = 512;
46 dev->size = mtd->size >> 9;
47 dev->tr = tr;
48 dev->readonly = 1;
50 add_mtd_blktrans_dev(dev);
51 }
53 static void mtdblock_remove_dev(struct mtd_blktrans_dev *dev)
54 {
55 del_mtd_blktrans_dev(dev);
56 kfree(dev);
57 }
59 static struct mtd_blktrans_ops mtdblock_tr = {
60 .name = "mtdblock",
61 .major = 31,
62 .part_bits = 0,
63 .readsect = mtdblock_readsect,
64 .writesect = mtdblock_writesect,
65 .add_mtd = mtdblock_add_mtd,
66 .remove_dev = mtdblock_remove_dev,
67 .owner = THIS_MODULE,
68 };
70 static int __init mtdblock_init(void)
71 {
72 return register_mtd_blktrans(&mtdblock_tr);
73 }
75 static void __exit mtdblock_exit(void)
76 {
77 deregister_mtd_blktrans(&mtdblock_tr);
78 }
80 module_init(mtdblock_init);
81 module_exit(mtdblock_exit);
83 MODULE_LICENSE("GPL");
84 MODULE_AUTHOR("David Woodhouse <dwmw2@infradead.org>");
85 MODULE_DESCRIPTION("Simple read-only block device emulation access to MTD devices");