view Documentation/debugging-modules.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 Debugging Modules after 2.6.3
2 -----------------------------
4 In almost all distributions, the kernel asks for modules which don't
5 exist, such as "net-pf-10" or whatever. Changing "modprobe -q" to
6 "succeed" in this case is hacky and breaks some setups, and also we
7 want to know if it failed for the fallback code for old aliases in
8 fs/char_dev.c, for example.
10 In the past a debugging message which would fill people's logs was
11 emitted. This debugging message has been removed. The correct way
12 of debugging module problems is something like this:
14 echo '#! /bin/sh' > /tmp/modprobe
15 echo 'echo "$@" >> /tmp/modprobe.log' >> /tmp/modprobe
16 echo 'exec /sbin/modprobe "$@"' >> /tmp/modprobe
17 chmod a+x /tmp/modprobe
18 echo /tmp/modprobe > /proc/sys/kernel/modprobe