view Documentation/networking/netconsole.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
2 started by Ingo Molnar <mingo@redhat.com>, 2001.09.17
3 2.6 port and netpoll api by Matt Mackall <mpm@selenic.com>, Sep 9 2003
5 Please send bug reports to Matt Mackall <mpm@selenic.com>
7 This module logs kernel printk messages over UDP allowing debugging of
8 problem where disk logging fails and serial consoles are impractical.
10 It can be used either built-in or as a module. As a built-in,
11 netconsole initializes immediately after NIC cards and will bring up
12 the specified interface as soon as possible. While this doesn't allow
13 capture of early kernel panics, it does capture most of the boot
14 process.
16 It takes a string configuration parameter "netconsole" in the
17 following format:
19 netconsole=[src-port]@[src-ip]/[<dev>],[tgt-port]@<tgt-ip>/[tgt-macaddr]
21 where
22 src-port source for UDP packets (defaults to 6665)
23 src-ip source IP to use (interface address)
24 dev network interface (eth0)
25 tgt-port port for logging agent (6666)
26 tgt-ip IP address for logging agent
27 tgt-macaddr ethernet MAC address for logging agent (broadcast)
29 Examples:
31 linux netconsole=4444@,9353@
33 or
35 insmod netconsole netconsole=@/,@
37 Built-in netconsole starts immediately after the TCP stack is
38 initialized and attempts to bring up the supplied dev at the supplied
39 address.
41 The remote host can run either 'netcat -u -l -p <port>' or syslogd.
43 WARNING: the default target ethernet setting uses the broadcast
44 ethernet address to send packets, which can cause increased load on
45 other systems on the same ethernet segment.
47 NOTE: the network device (eth1 in the above case) can run any kind
48 of other network traffic, netconsole is not intrusive. Netconsole
49 might cause slight delays in other traffic if the volume of kernel
50 messages is high, but should have no other impact.
52 Netconsole was designed to be as instantaneous as possible, to
53 enable the logging of even the most critical kernel bugs. It works
54 from IRQ contexts as well, and does not enable interrupts while
55 sending packets. Due to these unique needs, configuration can not
56 be more automatic, and some fundamental limitations will remain:
57 only IP networks, UDP packets and ethernet devices are supported.