view Documentation/cpu-freq/index.txt @ 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 CPU frequency and voltage scaling code in the Linux(TM) kernel
4 L i n u x C P U F r e q
9 Dominik Brodowski <linux@brodo.de>
13 Clock scaling allows you to change the clock speed of the CPUs on the
14 fly. This is a nice method to save battery power, because the lower
15 the clock speed, the less power the CPU consumes.
19 Documents in this directory:
20 ----------------------------
21 core.txt - General description of the CPUFreq core and
22 of CPUFreq notifiers
24 cpu-drivers.txt - How to implement a new cpufreq processor driver
26 governors.txt - What are cpufreq governors and how to
27 implement them?
29 index.txt - File index, Mailing list and Links (this document)
31 user-guide.txt - User Guide to CPUFreq
34 Mailing List
35 ------------
36 There is a CPU frequency changing CVS commit and general list where
37 you can report bugs, problems or submit patches. To post a message,
38 send an email to cpufreq@lists.linux.org.uk, to subscribe go to
39 http://lists.linux.org.uk/mailman/listinfo/cpufreq. Previous post to the
40 mailing list are available to subscribers at
41 http://lists.linux.org.uk/mailman/private/cpufreq/.
44 Links
45 -----
46 the FTP archives:
47 * ftp://ftp.linux.org.uk/pub/linux/cpufreq/
49 how to access the CVS repository:
50 * http://cvs.arm.linux.org.uk/
52 the CPUFreq Mailing list:
53 * http://lists.linux.org.uk/mailman/listinfo/cpufreq
55 Clock and voltage scaling for the SA-1100:
56 * http://www.lartmaker.nl/projects/scaling