view arch/m32r/Kconfig.debug @ 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 menu "Kernel hacking"
3 source "lib/Kconfig.debug"
6 bool "Check for stack overflows"
7 depends on DEBUG_KERNEL
8 help
9 This option will cause messages to be printed if free stack space
10 drops below a certain limit.
13 bool "Stack utilization instrumentation"
14 depends on DEBUG_KERNEL
15 help
16 Enables the display of the minimum amount of free stack which each
17 task has ever had available in the sysrq-T and sysrq-P debug output.
19 This option will slow down process creation somewhat.
22 bool "Debug page memory allocations"
23 depends on DEBUG_KERNEL && BROKEN
24 help
25 Unmap pages from the kernel linear mapping after free_pages().
26 This results in a large slowdown, but helps to find certain types
27 of memory corruptions.
30 bool "Compile the kernel with frame pointers"
31 help
32 If you say Y here the resulting kernel image will be slightly larger
33 and slower, but it will give very useful debugging information.
34 If you don't debug the kernel, you can say N, but we may not be able
35 to solve problems without frame pointers.
37 endmenu