ia64/linux-2.6.18-xen.hg

view arch/sparc/lib/atomic.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 /* atomic.S: Move this stuff here for better ICACHE hit rates.
2 *
3 * Copyright (C) 1996 David S. Miller (davem@caipfs.rutgers.edu)
4 */
6 #include <asm/ptrace.h>
7 #include <asm/psr.h>
9 .text
10 .align 4
12 .globl __atomic_begin
13 __atomic_begin:
15 #ifndef CONFIG_SMP
16 .globl ___xchg32_sun4c
17 ___xchg32_sun4c:
18 rd %psr, %g3
19 andcc %g3, PSR_PIL, %g0
20 bne 1f
21 nop
22 wr %g3, PSR_PIL, %psr
23 nop; nop; nop
24 1:
25 andcc %g3, PSR_PIL, %g0
26 ld [%g1], %g7
27 bne 1f
28 st %g2, [%g1]
29 wr %g3, 0x0, %psr
30 nop; nop; nop
31 1:
32 mov %g7, %g2
33 jmpl %o7 + 8, %g0
34 mov %g4, %o7
36 .globl ___xchg32_sun4md
37 ___xchg32_sun4md:
38 swap [%g1], %g2
39 jmpl %o7 + 8, %g0
40 mov %g4, %o7
41 #endif
43 /* Read asm-sparc/atomic.h carefully to understand how this works for SMP.
44 * Really, some things here for SMP are overly clever, go read the header.
45 */
46 .globl ___atomic24_add
47 ___atomic24_add:
48 rd %psr, %g3 ! Keep the code small, old way was stupid
49 nop; nop; nop; ! Let the bits set
50 or %g3, PSR_PIL, %g7 ! Disable interrupts
51 wr %g7, 0x0, %psr ! Set %psr
52 nop; nop; nop; ! Let the bits set
53 #ifdef CONFIG_SMP
54 1: ldstub [%g1 + 3], %g7 ! Spin on the byte lock for SMP.
55 orcc %g7, 0x0, %g0 ! Did we get it?
56 bne 1b ! Nope...
57 ld [%g1], %g7 ! Load locked atomic24_t
58 sra %g7, 8, %g7 ! Get signed 24-bit integer
59 add %g7, %g2, %g2 ! Add in argument
60 sll %g2, 8, %g7 ! Transpose back to atomic24_t
61 st %g7, [%g1] ! Clever: This releases the lock as well.
62 #else
63 ld [%g1], %g7 ! Load locked atomic24_t
64 add %g7, %g2, %g2 ! Add in argument
65 st %g2, [%g1] ! Store it back
66 #endif
67 wr %g3, 0x0, %psr ! Restore original PSR_PIL
68 nop; nop; nop; ! Let the bits set
69 jmpl %o7, %g0 ! NOTE: not + 8, see callers in atomic.h
70 mov %g4, %o7 ! Restore %o7
72 .globl ___atomic24_sub
73 ___atomic24_sub:
74 rd %psr, %g3 ! Keep the code small, old way was stupid
75 nop; nop; nop; ! Let the bits set
76 or %g3, PSR_PIL, %g7 ! Disable interrupts
77 wr %g7, 0x0, %psr ! Set %psr
78 nop; nop; nop; ! Let the bits set
79 #ifdef CONFIG_SMP
80 1: ldstub [%g1 + 3], %g7 ! Spin on the byte lock for SMP.
81 orcc %g7, 0x0, %g0 ! Did we get it?
82 bne 1b ! Nope...
83 ld [%g1], %g7 ! Load locked atomic24_t
84 sra %g7, 8, %g7 ! Get signed 24-bit integer
85 sub %g7, %g2, %g2 ! Subtract argument
86 sll %g2, 8, %g7 ! Transpose back to atomic24_t
87 st %g7, [%g1] ! Clever: This releases the lock as well
88 #else
89 ld [%g1], %g7 ! Load locked atomic24_t
90 sub %g7, %g2, %g2 ! Subtract argument
91 st %g2, [%g1] ! Store it back
92 #endif
93 wr %g3, 0x0, %psr ! Restore original PSR_PIL
94 nop; nop; nop; ! Let the bits set
95 jmpl %o7, %g0 ! NOTE: not + 8, see callers in atomic.h
96 mov %g4, %o7 ! Restore %o7
98 .globl __atomic_end
99 __atomic_end: