ia64/linux-2.6.18-xen.hg

view drivers/md/raid6algos.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
children
line source
1 /* -*- linux-c -*- ------------------------------------------------------- *
2 *
3 * Copyright 2002 H. Peter Anvin - All Rights Reserved
4 *
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License as published by
7 * the Free Software Foundation, Inc., 53 Temple Place Ste 330,
8 * Bostom MA 02111-1307, USA; either version 2 of the License, or
9 * (at your option) any later version; incorporated herein by reference.
10 *
11 * ----------------------------------------------------------------------- */
13 /*
14 * raid6algos.c
15 *
16 * Algorithm list and algorithm selection for RAID-6
17 */
19 #include "raid6.h"
20 #ifndef __KERNEL__
21 #include <sys/mman.h>
22 #include <stdio.h>
23 #endif
25 struct raid6_calls raid6_call;
27 /* Various routine sets */
28 extern const struct raid6_calls raid6_intx1;
29 extern const struct raid6_calls raid6_intx2;
30 extern const struct raid6_calls raid6_intx4;
31 extern const struct raid6_calls raid6_intx8;
32 extern const struct raid6_calls raid6_intx16;
33 extern const struct raid6_calls raid6_intx32;
34 extern const struct raid6_calls raid6_mmxx1;
35 extern const struct raid6_calls raid6_mmxx2;
36 extern const struct raid6_calls raid6_sse1x1;
37 extern const struct raid6_calls raid6_sse1x2;
38 extern const struct raid6_calls raid6_sse2x1;
39 extern const struct raid6_calls raid6_sse2x2;
40 extern const struct raid6_calls raid6_sse2x4;
41 extern const struct raid6_calls raid6_altivec1;
42 extern const struct raid6_calls raid6_altivec2;
43 extern const struct raid6_calls raid6_altivec4;
44 extern const struct raid6_calls raid6_altivec8;
46 const struct raid6_calls * const raid6_algos[] = {
47 &raid6_intx1,
48 &raid6_intx2,
49 &raid6_intx4,
50 &raid6_intx8,
51 #if defined(__ia64__)
52 &raid6_intx16,
53 &raid6_intx32,
54 #endif
55 #if defined(__i386__)
56 &raid6_mmxx1,
57 &raid6_mmxx2,
58 &raid6_sse1x1,
59 &raid6_sse1x2,
60 &raid6_sse2x1,
61 &raid6_sse2x2,
62 #endif
63 #if defined(__x86_64__)
64 &raid6_sse2x1,
65 &raid6_sse2x2,
66 &raid6_sse2x4,
67 #endif
68 #ifdef CONFIG_ALTIVEC
69 &raid6_altivec1,
70 &raid6_altivec2,
71 &raid6_altivec4,
72 &raid6_altivec8,
73 #endif
74 NULL
75 };
77 #ifdef __KERNEL__
78 #define RAID6_TIME_JIFFIES_LG2 4
79 #else
80 /* Need more time to be stable in userspace */
81 #define RAID6_TIME_JIFFIES_LG2 9
82 #endif
84 /* Try to pick the best algorithm */
85 /* This code uses the gfmul table as convenient data set to abuse */
87 int __init raid6_select_algo(void)
88 {
89 const struct raid6_calls * const * algo;
90 const struct raid6_calls * best;
91 char *syndromes;
92 void *dptrs[(65536/PAGE_SIZE)+2];
93 int i, disks;
94 unsigned long perf, bestperf;
95 int bestprefer;
96 unsigned long j0, j1;
98 disks = (65536/PAGE_SIZE)+2;
99 for ( i = 0 ; i < disks-2 ; i++ ) {
100 dptrs[i] = ((char *)raid6_gfmul) + PAGE_SIZE*i;
101 }
103 /* Normal code - use a 2-page allocation to avoid D$ conflict */
104 syndromes = (void *) __get_free_pages(GFP_KERNEL, 1);
106 if ( !syndromes ) {
107 printk("raid6: Yikes! No memory available.\n");
108 return -ENOMEM;
109 }
111 dptrs[disks-2] = syndromes;
112 dptrs[disks-1] = syndromes + PAGE_SIZE;
114 bestperf = 0; bestprefer = 0; best = NULL;
116 for ( algo = raid6_algos ; *algo ; algo++ ) {
117 if ( !(*algo)->valid || (*algo)->valid() ) {
118 perf = 0;
120 preempt_disable();
121 j0 = jiffies;
122 while ( (j1 = jiffies) == j0 )
123 cpu_relax();
124 while ( (jiffies-j1) < (1 << RAID6_TIME_JIFFIES_LG2) ) {
125 (*algo)->gen_syndrome(disks, PAGE_SIZE, dptrs);
126 perf++;
127 }
128 preempt_enable();
130 if ( (*algo)->prefer > bestprefer ||
131 ((*algo)->prefer == bestprefer &&
132 perf > bestperf) ) {
133 best = *algo;
134 bestprefer = best->prefer;
135 bestperf = perf;
136 }
137 printk("raid6: %-8s %5ld MB/s\n", (*algo)->name,
138 (perf*HZ) >> (20-16+RAID6_TIME_JIFFIES_LG2));
139 }
140 }
142 if (best) {
143 printk("raid6: using algorithm %s (%ld MB/s)\n",
144 best->name,
145 (bestperf*HZ) >> (20-16+RAID6_TIME_JIFFIES_LG2));
146 raid6_call = *best;
147 } else
148 printk("raid6: Yikes! No algorithm found!\n");
150 free_pages((unsigned long)syndromes, 1);
152 return best ? 0 : -EINVAL;
153 }