view Documentation/networking/ncsa-telnet @ 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 NCSA telnet doesn't work with path MTU discovery enabled. This is due to a
2 bug in NCSA that also stops it working with other modern networking code
3 such as Solaris.
5 The following information is courtesy of
6 Marek <marekm@i17linuxb.ists.pwr.wroc.pl>
8 There is a fixed version somewhere on ftp.upe.ac.za (sorry, I don't
9 remember the exact pathname, and this site is very slow from here).
10 It may or may not be faster for you to get it from
11 ftp://ftp.ists.pwr.wroc.pl/pub/msdos/telnet/ncsa_upe/tel23074.zip
12 (source is in v230704s.zip). I have tested it with 1.3.79 (with
13 path mtu discovery enabled - ncsa 2.3.08 didn't work) and it seems
14 to work. I don't know if anyone is working on this code - this
15 version is over a year old. Too bad - it's faster and often more
16 stable than these windoze telnets, and runs on almost anything...