view lib/iomap_copy.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
line source
1 /*
2 * Copyright 2006 PathScale, Inc. All Rights Reserved.
3 *
4 * This file is free software; you can redistribute it and/or modify
5 * it under the terms of version 2 of the GNU General Public License
6 * as published by the Free Software Foundation.
7 *
8 * This program is distributed in the hope that it will be useful,
9 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * GNU General Public License for more details.
12 *
13 * You should have received a copy of the GNU General Public License
14 * along with this program; if not, write to the Free Software Foundation,
15 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.
16 */
18 #include <linux/module.h>
19 #include <linux/io.h>
21 /**
22 * __iowrite32_copy - copy data to MMIO space, in 32-bit units
23 * @to: destination, in MMIO space (must be 32-bit aligned)
24 * @from: source (must be 32-bit aligned)
25 * @count: number of 32-bit quantities to copy
26 *
27 * Copy data from kernel space to MMIO space, in units of 32 bits at a
28 * time. Order of access is not guaranteed, nor is a memory barrier
29 * performed afterwards.
30 */
31 void __attribute__((weak)) __iowrite32_copy(void __iomem *to,
32 const void *from,
33 size_t count)
34 {
35 u32 __iomem *dst = to;
36 const u32 *src = from;
37 const u32 *end = src + count;
39 while (src < end)
40 __raw_writel(*src++, dst++);
41 }
42 EXPORT_SYMBOL_GPL(__iowrite32_copy);
44 /**
45 * __iowrite64_copy - copy data to MMIO space, in 64-bit or 32-bit units
46 * @to: destination, in MMIO space (must be 64-bit aligned)
47 * @from: source (must be 64-bit aligned)
48 * @count: number of 64-bit quantities to copy
49 *
50 * Copy data from kernel space to MMIO space, in units of 32 or 64 bits at a
51 * time. Order of access is not guaranteed, nor is a memory barrier
52 * performed afterwards.
53 */
54 void __attribute__((weak)) __iowrite64_copy(void __iomem *to,
55 const void *from,
56 size_t count)
57 {
58 #ifdef CONFIG_64BIT
59 u64 __iomem *dst = to;
60 const u64 *src = from;
61 const u64 *end = src + count;
63 while (src < end)
64 __raw_writeq(*src++, dst++);
65 #else
66 __iowrite32_copy(to, from, count * 2);
67 #endif
68 }
70 EXPORT_SYMBOL_GPL(__iowrite64_copy);