view Documentation/networking/ip_dynaddr.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 IP dynamic address hack-port v0.03
2 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
3 This stuff allows diald ONESHOT connections to get established by
4 dynamically changing packet source address (and socket's if local procs).
5 It is implemented for TCP diald-box connections(1) and IP_MASQuerading(2).
7 If enabled[*] and forwarding interface has changed:
8 1) Socket (and packet) source address is rewritten ON RETRANSMISSIONS
9 while in SYN_SENT state (diald-box processes).
10 2) Out-bounded MASQueraded source address changes ON OUTPUT (when
11 internal host does retransmission) until a packet from outside is
12 received by the tunnel.
14 This is specially helpful for auto dialup links (diald), where the
15 ``actual'' outgoing address is unknown at the moment the link is
16 going up. So, the *same* (local AND masqueraded) connections requests that
17 bring the link up will be able to get established.
19 [*] At boot, by default no address rewriting is attempted.
20 To enable:
21 # echo 1 > /proc/sys/net/ipv4/ip_dynaddr
22 To enable verbose mode:
23 # echo 2 > /proc/sys/net/ipv4/ip_dynaddr
24 To disable (default)
25 # echo 0 > /proc/sys/net/ipv4/ip_dynaddr
27 Enjoy!
29 -- Juanjo <jjciarla@raiz.uncu.edu.ar>