view Documentation/riscom8.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 * NOTE - this is an unmaintained driver. The original author cannot be located.
3 SDL Communications is now SBS Technologies, and does not have any
4 information on these ancient ISA cards on their website.
6 James Nelson <james4765@gmail.com> - 12-12-2004
8 This is the README for RISCom/8 multi-port serial driver
9 (C) 1994-1996 D.Gorodchanin
10 See file LICENSE for terms and conditions.
12 NOTE: English is not my native language.
13 I'm sorry for any mistakes in this text.
15 Misc. notes for RISCom/8 serial driver, in no particular order :)
17 1) This driver can support up to 4 boards at time.
18 Use string "riscom8=0xXXX,0xXXX,0xXXX,0xXXX" at LILO prompt, for
19 setting I/O base addresses for boards. If you compile driver
20 as module use modprobe options "iobase=0xXXX iobase1=0xXXX iobase2=..."
22 2) The driver partially supports famous 'setserial' program, you can use almost
23 any of its options, excluding port & irq settings.
25 3) There are some misc. defines at the beginning of riscom8.c, please read the
26 comments and try to change some of them in case of problems.
28 4) I consider the current state of the driver as BETA.
30 5) SDL Communications WWW page is http://www.sdlcomm.com.
32 6) You can use the MAKEDEV program to create RISCom/8 /dev/ttyL* entries.
34 7) Minor numbers for first board are 0-7, for second 8-15, etc.
36 22 Apr 1996.