view Documentation/networking/x25.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 Linux X.25 Project
3 As my third year dissertation at University I have taken it upon myself to
4 write an X.25 implementation for Linux. My aim is to provide a complete X.25
5 Packet Layer and a LAPB module to allow for "normal" X.25 to be run using
6 Linux. There are two sorts of X.25 cards available, intelligent ones that
7 implement LAPB on the card itself, and unintelligent ones that simply do
8 framing, bit-stuffing and checksumming. These both need to be handled by the
9 system.
11 I therefore decided to write the implementation such that as far as the
12 Packet Layer is concerned, the link layer was being performed by a lower
13 layer of the Linux kernel and therefore it did not concern itself with
14 implementation of LAPB. Therefore the LAPB modules would be called by
15 unintelligent X.25 card drivers and not by intelligent ones, this would
16 provide a uniform device driver interface, and simplify configuration.
18 To confuse matters a little, an 802.2 LLC implementation for Linux is being
19 written which will allow X.25 to be run over an Ethernet (or Token Ring) and
20 conform with the JNT "Pink Book", this will have a different interface to
21 the Packet Layer but there will be no confusion since the class of device
22 being served by the LLC will be completely separate from LAPB. The LLC
23 implementation is being done as part of another protocol project (SNA) and
24 by a different author.
26 Just when you thought that it could not become more confusing, another
27 option appeared, XOT. This allows X.25 Packet Layer frames to operate over
28 the Internet using TCP/IP as a reliable link layer. RFC1613 specifies the
29 format and behaviour of the protocol. If time permits this option will also
30 be actively considered.
32 A linux-x25 mailing list has been created at vger.kernel.org to support the
33 development and use of Linux X.25. It is early days yet, but interested
34 parties are welcome to subscribe to it. Just send a message to
35 majordomo@vger.kernel.org with the following in the message body:
37 subscribe linux-x25
38 end
40 The contents of the Subject line are ignored.
42 Jonathan
44 g4klx@g4klx.demon.co.uk