view arch/sparc/lib/bitops.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
line source
1 /* bitops.S: Low level assembler bit operations.
2 *
3 * Copyright (C) 1996 David S. Miller (davem@caip.rutgers.edu)
4 */
6 #include <asm/ptrace.h>
7 #include <asm/psr.h>
9 .text
10 .align 4
12 .globl __bitops_begin
13 __bitops_begin:
15 /* Take bits in %g2 and set them in word at %g1,
16 * return whether bits were set in original value
17 * in %g2. %g4 holds value to restore into %o7
18 * in delay slot of jmpl return, %g3 + %g5 + %g7 can be
19 * used as temporaries and thus is considered clobbered
20 * by all callers.
21 */
22 .globl ___set_bit
23 ___set_bit:
24 rd %psr, %g3
25 nop; nop; nop;
26 or %g3, PSR_PIL, %g5
27 wr %g5, 0x0, %psr
28 nop; nop; nop
29 #ifdef CONFIG_SMP
30 set bitops_spinlock, %g5
31 2: ldstub [%g5], %g7 ! Spin on the byte lock for SMP.
32 orcc %g7, 0x0, %g0 ! Did we get it?
33 bne 2b ! Nope...
34 #endif
35 ld [%g1], %g7
36 or %g7, %g2, %g5
37 and %g7, %g2, %g2
38 #ifdef CONFIG_SMP
39 st %g5, [%g1]
40 set bitops_spinlock, %g5
41 stb %g0, [%g5]
42 #else
43 st %g5, [%g1]
44 #endif
45 wr %g3, 0x0, %psr
46 nop; nop; nop
47 jmpl %o7, %g0
48 mov %g4, %o7
50 /* Same as above, but clears the bits from %g2 instead. */
51 .globl ___clear_bit
52 ___clear_bit:
53 rd %psr, %g3
54 nop; nop; nop
55 or %g3, PSR_PIL, %g5
56 wr %g5, 0x0, %psr
57 nop; nop; nop
58 #ifdef CONFIG_SMP
59 set bitops_spinlock, %g5
60 2: ldstub [%g5], %g7 ! Spin on the byte lock for SMP.
61 orcc %g7, 0x0, %g0 ! Did we get it?
62 bne 2b ! Nope...
63 #endif
64 ld [%g1], %g7
65 andn %g7, %g2, %g5
66 and %g7, %g2, %g2
67 #ifdef CONFIG_SMP
68 st %g5, [%g1]
69 set bitops_spinlock, %g5
70 stb %g0, [%g5]
71 #else
72 st %g5, [%g1]
73 #endif
74 wr %g3, 0x0, %psr
75 nop; nop; nop
76 jmpl %o7, %g0
77 mov %g4, %o7
79 /* Same thing again, but this time toggles the bits from %g2. */
80 .globl ___change_bit
81 ___change_bit:
82 rd %psr, %g3
83 nop; nop; nop
84 or %g3, PSR_PIL, %g5
85 wr %g5, 0x0, %psr
86 nop; nop; nop
87 #ifdef CONFIG_SMP
88 set bitops_spinlock, %g5
89 2: ldstub [%g5], %g7 ! Spin on the byte lock for SMP.
90 orcc %g7, 0x0, %g0 ! Did we get it?
91 bne 2b ! Nope...
92 #endif
93 ld [%g1], %g7
94 xor %g7, %g2, %g5
95 and %g7, %g2, %g2
96 #ifdef CONFIG_SMP
97 st %g5, [%g1]
98 set bitops_spinlock, %g5
99 stb %g0, [%g5]
100 #else
101 st %g5, [%g1]
102 #endif
103 wr %g3, 0x0, %psr
104 nop; nop; nop
105 jmpl %o7, %g0
106 mov %g4, %o7
108 .globl __bitops_end
109 __bitops_end: