ia64/linux-2.6.18-xen.hg

view Documentation/sgi-visws.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
children
line source
2 The SGI Visual Workstations (models 320 and 540) are based around
3 the Cobalt, Lithium, and Arsenic ASICs. The Cobalt ASIC is the
4 main system ASIC which interfaces the 1-4 IA32 cpus, the memory
5 system, and the I/O system in the Lithium ASIC. The Cobalt ASIC
6 also contains the 3D gfx rendering engine which renders to main
7 system memory -- part of which is used as the frame buffer which
8 is DMA'ed to a video connector using the Arsenic ASIC. A PIIX4
9 chip and NS87307 are used to provide legacy device support (IDE,
10 serial, floppy, and parallel).
12 The Visual Workstation chipset largely conforms to the PC architecture
13 with some notable exceptions such as interrupt handling.