view arch/sparc/prom/palloc.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 /* $Id: palloc.c,v 1.4 1996/04/25 06:09:48 davem Exp $
2 * palloc.c: Memory allocation from the Sun PROM.
3 *
4 * Copyright (C) 1995 David S. Miller (davem@caip.rutgers.edu)
5 */
7 #include <asm/openprom.h>
8 #include <asm/oplib.h>
10 /* You should not call these routines after memory management
11 * has been initialized in the kernel, if fact you should not
12 * use these if at all possible in the kernel. They are mainly
13 * to be used for a bootloader for temporary allocations which
14 * it will free before jumping into the kernel it has loaded.
15 *
16 * Also, these routines don't work on V0 proms, only V2 and later.
17 */
19 /* Allocate a chunk of memory of size 'num_bytes' giving a suggestion
20 * of virtual_hint as the preferred virtual base address of this chunk.
21 * There are no guarantees that you will get the allocation, or that
22 * the prom will abide by your "hint". So check your return value.
23 */
24 char *
25 prom_alloc(char *virtual_hint, unsigned int num_bytes)
26 {
27 if(prom_vers == PROM_V0) return (char *) 0x0;
28 if(num_bytes == 0x0) return (char *) 0x0;
29 return (*(romvec->pv_v2devops.v2_dumb_mem_alloc))(virtual_hint, num_bytes);
30 }
32 /* Free a previously allocated chunk back to the prom at virtual address
33 * 'vaddr' of size 'num_bytes'. NOTE: This vaddr is not the hint you
34 * used for the allocation, but the virtual address the prom actually
35 * returned to you. They may be have been the same, they may have not,
36 * doesn't matter.
37 */
38 void
39 prom_free(char *vaddr, unsigned int num_bytes)
40 {
41 if((prom_vers == PROM_V0) || (num_bytes == 0x0)) return;
42 (*(romvec->pv_v2devops.v2_dumb_mem_free))(vaddr, num_bytes);
43 return;
44 }