view lib/crc32defs.h @ 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 /*
2 * There are multiple 16-bit CRC polynomials in common use, but this is
3 * *the* standard CRC-32 polynomial, first popularized by Ethernet.
4 * x^32+x^26+x^23+x^22+x^16+x^12+x^11+x^10+x^8+x^7+x^5+x^4+x^2+x^1+x^0
5 */
6 #define CRCPOLY_LE 0xedb88320
7 #define CRCPOLY_BE 0x04c11db7
9 /* How many bits at a time to use. Requires a table of 4<<CRC_xx_BITS bytes. */
10 /* For less performance-sensitive, use 4 */
11 #ifndef CRC_LE_BITS
12 # define CRC_LE_BITS 8
13 #endif
14 #ifndef CRC_BE_BITS
15 # define CRC_BE_BITS 8
16 #endif
18 /*
19 * Little-endian CRC computation. Used with serial bit streams sent
20 * lsbit-first. Be sure to use cpu_to_le32() to append the computed CRC.
21 */
22 #if CRC_LE_BITS > 8 || CRC_LE_BITS < 1 || CRC_LE_BITS & CRC_LE_BITS-1
23 # error CRC_LE_BITS must be a power of 2 between 1 and 8
24 #endif
26 /*
27 * Big-endian CRC computation. Used with serial bit streams sent
28 * msbit-first. Be sure to use cpu_to_be32() to append the computed CRC.
29 */
30 #if CRC_BE_BITS > 8 || CRC_BE_BITS < 1 || CRC_BE_BITS & CRC_BE_BITS-1
31 # error CRC_BE_BITS must be a power of 2 between 1 and 8
32 #endif