view Documentation/cpu-freq/cpufreq-nforce2.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
2 The cpufreq-nforce2 driver changes the FSB on nVidia nForce2 plattforms.
4 This works better than on other plattforms, because the FSB of the CPU
5 can be controlled independently from the PCI/AGP clock.
7 The module has two options:
9 fid: multiplier * 10 (for example 8.5 = 85)
10 min_fsb: minimum FSB
12 If not set, fid is calculated from the current CPU speed and the FSB.
13 min_fsb defaults to FSB at boot time - 50 MHz.
15 IMPORTANT: The available range is limited downwards!
16 Also the minimum available FSB can differ, for systems
17 booting with 200 MHz, 150 should always work.