ia64/linux-2.6.18-xen.hg

view lib/halfmd4.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 #include <linux/kernel.h>
2 #include <linux/module.h>
3 #include <linux/cryptohash.h>
5 /* F, G and H are basic MD4 functions: selection, majority, parity */
6 #define F(x, y, z) ((z) ^ ((x) & ((y) ^ (z))))
7 #define G(x, y, z) (((x) & (y)) + (((x) ^ (y)) & (z)))
8 #define H(x, y, z) ((x) ^ (y) ^ (z))
10 /*
11 * The generic round function. The application is so specific that
12 * we don't bother protecting all the arguments with parens, as is generally
13 * good macro practice, in favor of extra legibility.
14 * Rotation is separate from addition to prevent recomputation
15 */
16 #define ROUND(f, a, b, c, d, x, s) \
17 (a += f(b, c, d) + x, a = (a << s) | (a >> (32 - s)))
18 #define K1 0
19 #define K2 013240474631UL
20 #define K3 015666365641UL
22 /*
23 * Basic cut-down MD4 transform. Returns only 32 bits of result.
24 */
25 __u32 half_md4_transform(__u32 buf[4], __u32 const in[8])
26 {
27 __u32 a = buf[0], b = buf[1], c = buf[2], d = buf[3];
29 /* Round 1 */
30 ROUND(F, a, b, c, d, in[0] + K1, 3);
31 ROUND(F, d, a, b, c, in[1] + K1, 7);
32 ROUND(F, c, d, a, b, in[2] + K1, 11);
33 ROUND(F, b, c, d, a, in[3] + K1, 19);
34 ROUND(F, a, b, c, d, in[4] + K1, 3);
35 ROUND(F, d, a, b, c, in[5] + K1, 7);
36 ROUND(F, c, d, a, b, in[6] + K1, 11);
37 ROUND(F, b, c, d, a, in[7] + K1, 19);
39 /* Round 2 */
40 ROUND(G, a, b, c, d, in[1] + K2, 3);
41 ROUND(G, d, a, b, c, in[3] + K2, 5);
42 ROUND(G, c, d, a, b, in[5] + K2, 9);
43 ROUND(G, b, c, d, a, in[7] + K2, 13);
44 ROUND(G, a, b, c, d, in[0] + K2, 3);
45 ROUND(G, d, a, b, c, in[2] + K2, 5);
46 ROUND(G, c, d, a, b, in[4] + K2, 9);
47 ROUND(G, b, c, d, a, in[6] + K2, 13);
49 /* Round 3 */
50 ROUND(H, a, b, c, d, in[3] + K3, 3);
51 ROUND(H, d, a, b, c, in[7] + K3, 9);
52 ROUND(H, c, d, a, b, in[2] + K3, 11);
53 ROUND(H, b, c, d, a, in[6] + K3, 15);
54 ROUND(H, a, b, c, d, in[1] + K3, 3);
55 ROUND(H, d, a, b, c, in[5] + K3, 9);
56 ROUND(H, c, d, a, b, in[0] + K3, 11);
57 ROUND(H, b, c, d, a, in[4] + K3, 15);
59 buf[0] += a;
60 buf[1] += b;
61 buf[2] += c;
62 buf[3] += d;
64 return buf[1]; /* "most hashed" word */
65 }
66 EXPORT_SYMBOL(half_md4_transform);