ia64/linux-2.6.18-xen.hg

view arch/sparc64/kernel/dtlb_prot.S @ 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 /* $Id: dtlb_prot.S,v 1.22 2001/04/11 23:40:32 davem Exp $
2 * dtlb_prot.S: DTLB protection trap strategy.
3 * This is included directly into the trap table.
4 *
5 * Copyright (C) 1996,1998 David S. Miller (davem@redhat.com)
6 * Copyright (C) 1997,1998 Jakub Jelinek (jj@ultra.linux.cz)
7 */
9 /* Ways we can get here:
10 *
11 * [TL == 0] 1) User stores to readonly pages.
12 * [TL == 0] 2) Nucleus stores to user readonly pages.
13 * [TL > 0] 3) Nucleus stores to user readonly stack frame.
14 */
16 /* PROT ** ICACHE line 1: User DTLB protection trap */
17 mov TLB_SFSR, %g1
18 stxa %g0, [%g1] ASI_DMMU ! Clear FaultValid bit
19 membar #Sync ! Synchronize stores
20 rdpr %pstate, %g5 ! Move into alt-globals
21 wrpr %g5, PSTATE_AG|PSTATE_MG, %pstate
22 rdpr %tl, %g1 ! Need a winfixup?
23 cmp %g1, 1 ! Trap level >1?
24 mov TLB_TAG_ACCESS, %g4 ! For reload of vaddr
26 /* PROT ** ICACHE line 2: More real fault processing */
27 bgu,pn %xcc, winfix_trampoline ! Yes, perform winfixup
28 ldxa [%g4] ASI_DMMU, %g5 ! Put tagaccess in %g5
29 ba,pt %xcc, sparc64_realfault_common ! Nope, normal fault
30 mov FAULT_CODE_DTLB | FAULT_CODE_WRITE, %g4
31 nop
32 nop
33 nop
34 nop
36 /* PROT ** ICACHE line 3: Unused... */
37 nop
38 nop
39 nop
40 nop
41 nop
42 nop
43 nop
44 nop
46 /* PROT ** ICACHE line 4: Unused... */
47 nop
48 nop
49 nop
50 nop
51 nop
52 nop
53 nop
54 nop