ia64/linux-2.6.18-xen.hg

view drivers/md/raid6int.uc @ 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 2002-2004 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 * raid6int$#.c
15 *
16 * $#-way unrolled portable integer math RAID-6 instruction set
17 *
18 * This file is postprocessed using unroll.pl
19 */
21 #include "raid6.h"
23 /*
24 * This is the C data type to use
25 */
27 /* Change this from BITS_PER_LONG if there is something better... */
28 #if BITS_PER_LONG == 64
29 # define NBYTES(x) ((x) * 0x0101010101010101UL)
30 # define NSIZE 8
31 # define NSHIFT 3
32 # define NSTRING "64"
33 typedef u64 unative_t;
34 #else
35 # define NBYTES(x) ((x) * 0x01010101U)
36 # define NSIZE 4
37 # define NSHIFT 2
38 # define NSTRING "32"
39 typedef u32 unative_t;
40 #endif
44 /*
45 * IA-64 wants insane amounts of unrolling. On other architectures that
46 * is just a waste of space.
47 */
48 #if ($# <= 8) || defined(__ia64__)
51 /*
52 * These sub-operations are separate inlines since they can sometimes be
53 * specially optimized using architecture-specific hacks.
54 */
56 /*
57 * The SHLBYTE() operation shifts each byte left by 1, *not*
58 * rolling over into the next byte
59 */
60 static inline __attribute_const__ unative_t SHLBYTE(unative_t v)
61 {
62 unative_t vv;
64 vv = (v << 1) & NBYTES(0xfe);
65 return vv;
66 }
68 /*
69 * The MASK() operation returns 0xFF in any byte for which the high
70 * bit is 1, 0x00 for any byte for which the high bit is 0.
71 */
72 static inline __attribute_const__ unative_t MASK(unative_t v)
73 {
74 unative_t vv;
76 vv = v & NBYTES(0x80);
77 vv = (vv << 1) - (vv >> 7); /* Overflow on the top bit is OK */
78 return vv;
79 }
82 static void raid6_int$#_gen_syndrome(int disks, size_t bytes, void **ptrs)
83 {
84 u8 **dptr = (u8 **)ptrs;
85 u8 *p, *q;
86 int d, z, z0;
88 unative_t wd$$, wq$$, wp$$, w1$$, w2$$;
90 z0 = disks - 3; /* Highest data disk */
91 p = dptr[z0+1]; /* XOR parity */
92 q = dptr[z0+2]; /* RS syndrome */
94 for ( d = 0 ; d < bytes ; d += NSIZE*$# ) {
95 wq$$ = wp$$ = *(unative_t *)&dptr[z0][d+$$*NSIZE];
96 for ( z = z0-1 ; z >= 0 ; z-- ) {
97 wd$$ = *(unative_t *)&dptr[z][d+$$*NSIZE];
98 wp$$ ^= wd$$;
99 w2$$ = MASK(wq$$);
100 w1$$ = SHLBYTE(wq$$);
101 w2$$ &= NBYTES(0x1d);
102 w1$$ ^= w2$$;
103 wq$$ = w1$$ ^ wd$$;
104 }
105 *(unative_t *)&p[d+NSIZE*$$] = wp$$;
106 *(unative_t *)&q[d+NSIZE*$$] = wq$$;
107 }
108 }
110 const struct raid6_calls raid6_intx$# = {
111 raid6_int$#_gen_syndrome,
112 NULL, /* always valid */
113 "int" NSTRING "x$#",
114 0
115 };
117 #endif