view Documentation/stable_kernel_rules.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 Everything you ever wanted to know about Linux 2.6 -stable releases.
3 Rules on what kind of patches are accepted, and which ones are not, into the
4 "-stable" tree:
6 - It must be obviously correct and tested.
7 - It can not be bigger than 100 lines, with context.
8 - It must fix only one thing.
9 - It must fix a real bug that bothers people (not a, "This could be a
10 problem..." type thing).
11 - It must fix a problem that causes a build error (but not for things
12 marked CONFIG_BROKEN), an oops, a hang, data corruption, a real
13 security issue, or some "oh, that's not good" issue. In short, something
14 critical.
15 - No "theoretical race condition" issues, unless an explanation of how the
16 race can be exploited is also provided.
17 - It can not contain any "trivial" fixes in it (spelling changes,
18 whitespace cleanups, etc).
19 - It must be accepted by the relevant subsystem maintainer.
20 - It must follow the Documentation/SubmittingPatches rules.
23 Procedure for submitting patches to the -stable tree:
25 - Send the patch, after verifying that it follows the above rules, to
26 stable@kernel.org.
27 - The sender will receive an ACK when the patch has been accepted into the
28 queue, or a NAK if the patch is rejected. This response might take a few
29 days, according to the developer's schedules.
30 - If accepted, the patch will be added to the -stable queue, for review by
31 other developers.
32 - Security patches should not be sent to this alias, but instead to the
33 documented security@kernel.org address.
36 Review cycle:
38 - When the -stable maintainers decide for a review cycle, the patches will be
39 sent to the review committee, and the maintainer of the affected area of
40 the patch (unless the submitter is the maintainer of the area) and CC: to
41 the linux-kernel mailing list.
42 - The review committee has 48 hours in which to ACK or NAK the patch.
43 - If the patch is rejected by a member of the committee, or linux-kernel
44 members object to the patch, bringing up issues that the maintainers and
45 members did not realize, the patch will be dropped from the queue.
46 - At the end of the review cycle, the ACKed patches will be added to the
47 latest -stable release, and a new -stable release will happen.
48 - Security patches will be accepted into the -stable tree directly from the
49 security kernel team, and not go through the normal review cycle.
50 Contact the kernel security team for more details on this procedure.
53 Review committe:
55 - This is made up of a number of kernel developers who have volunteered for
56 this task, and a few that haven't.