view drivers/net/LICENSE.SRC @ 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 Code in this directory written at the IDA Supercomputing Research Center
2 carries the following copyright and license.
4 Copyright 1993 United States Government as represented by the
5 Director, National Security Agency. This software may be used
6 and distributed according to the terms of the GNU General Public License,
7 incorporated herein by reference.
9 In addition to the disclaimers in the GPL, SRC expressly disclaims any
10 and all warranties, expressed or implied, concerning the enclosed software.
11 This software was developed at SRC for use in internal research, and the
12 intent in sharing this software is to promote the productive interchange
13 of ideas throughout the research community. All software is furnished
14 on an "as-is" basis. No further updates to this software should be
15 expected. Although updates may occur, no commitment exists.