view Documentation/smp.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 To set up SMP
3 Configure the kernel and answer Y to CONFIG_SMP.
5 If you are using LILO, it is handy to have both SMP and non-SMP
6 kernel images on hand. Edit /etc/lilo.conf to create an entry
7 for another kernel image called "linux-smp" or something.
9 The next time you compile the kernel, when running a SMP kernel,
10 edit linux/Makefile and change "MAKE=make" to "MAKE=make -jN"
11 (where N = number of CPU + 1, or if you have tons of memory/swap
12 you can just use "-j" without a number). Feel free to experiment
13 with this one.
15 Of course you should time how long each build takes :-)
16 Example:
17 make config
18 time -v sh -c 'make clean install modules modules_install'
20 If you are using some Compaq MP compliant machines you will need to set
21 the operating system in the BIOS settings to "Unixware" - don't ask me
22 why Compaqs don't work otherwise.