view Documentation/networking/sctp.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 Kernel SCTP
3 This is the current BETA release of the Linux Kernel SCTP reference
4 implementation.
6 SCTP (Stream Control Transmission Protocol) is a IP based, message oriented,
7 reliable transport protocol, with congestion control, support for
8 transparent multi-homing, and multiple ordered streams of messages.
9 RFC2960 defines the core protocol. The IETF SIGTRAN working group originally
10 developed the SCTP protocol and later handed the protocol over to the
11 Transport Area (TSVWG) working group for the continued evolvement of SCTP as a
12 general purpose transport.
14 See the IETF website (http://www.ietf.org) for further documents on SCTP.
15 See http://www.ietf.org/rfc/rfc2960.txt
17 The initial project goal is to create an Linux kernel reference implementation
18 of SCTP that is RFC 2960 compliant and provides an programming interface
19 referred to as the UDP-style API of the Sockets Extensions for SCTP, as
20 proposed in IETF Internet-Drafts.
23 Caveats:
25 -lksctp can be built as statically or as a module. However, be aware that
26 module removal of lksctp is not yet a safe activity.
28 -There is tentative support for IPv6, but most work has gone towards
29 implementation and testing lksctp on IPv4.
32 For more information, please visit the lksctp project website:
33 http://www.sf.net/projects/lksctp
35 Or contact the lksctp developers through the mailing list:
36 <lksctp-developers@lists.sourceforge.net>