view Documentation/networking/decnet.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 DECnet Networking Layer Information
2 ===========================================
4 1) Other documentation....
6 o Project Home Pages
7 http://www.chygwyn.com/DECnet/ - Kernel info
8 http://linux-decnet.sourceforge.net/ - Userland tools
9 http://www.sourceforge.net/projects/linux-decnet/ - Status page
11 2) Configuring the kernel
13 Be sure to turn on the following options:
15 CONFIG_DECNET (obviously)
16 CONFIG_PROC_FS (to see what's going on)
17 CONFIG_SYSCTL (for easy configuration)
19 if you want to try out router support (not properly debugged yet)
20 you'll need the following options as well...
22 CONFIG_DECNET_ROUTER (to be able to add/delete routes)
23 CONFIG_NETFILTER (will be required for the DECnet routing daemon)
27 Don't turn on SIOCGIFCONF support for DECnet unless you are really sure
28 that you need it, in general you won't and it can cause ifconfig to
29 malfunction.
31 Run time configuration has changed slightly from the 2.4 system. If you
32 want to configure an endnode, then the simplified procedure is as follows:
34 o Set the MAC address on your ethernet card before starting _any_ other
35 network protocols.
37 As soon as your network card is brought into the UP state, DECnet should
38 start working. If you need something more complicated or are unsure how
39 to set the MAC address, see the next section. Also all configurations which
40 worked with 2.4 will work under 2.5 with no change.
42 3) Command line options
44 You can set a DECnet address on the kernel command line for compatibility
45 with the 2.4 configuration procedure, but in general it's not needed any more.
46 If you do st a DECnet address on the command line, it has only one purpose
47 which is that its added to the addresses on the loopback device.
49 With 2.4 kernels, DECnet would only recognise addresses as local if they
50 were added to the loopback device. In 2.5, any local interface address
51 can be used to loop back to the local machine. Of course this does not
52 prevent you adding further addresses to the loopback device if you
53 want to.
55 N.B. Since the address list of an interface determines the addresses for
56 which "hello" messages are sent, if you don't set an address on the loopback
57 interface then you won't see any entries in /proc/net/neigh for the local
58 host until such time as you start a connection. This doesn't affect the
59 operation of the local communications in any other way though.
61 The kernel command line takes options looking like the following:
63 decnet=1,2
65 the two numbers are the node address 1,2 = 1.2 For 2.2.xx kernels
66 and early 2.3.xx kernels, you must use a comma when specifying the
67 DECnet address like this. For more recent 2.3.xx kernels, you may
68 use almost any character except space, although a `.` would be the most
69 obvious choice :-)
71 There used to be a third number specifying the node type. This option
72 has gone away in favour of a per interface node type. This is now set
73 using /proc/sys/net/decnet/conf/<dev>/forwarding. This file can be
74 set with a single digit, 0=EndNode, 1=L1 Router and 2=L2 Router.
76 There are also equivalent options for modules. The node address can
77 also be set through the /proc/sys/net/decnet/ files, as can other system
78 parameters.
80 Currently the only supported devices are ethernet and ip_gre. The
81 ethernet address of your ethernet card has to be set according to the DECnet
82 address of the node in order for it to be autoconfigured (and then appear in
83 /proc/net/decnet_dev). There is a utility available at the above
84 FTP sites called dn2ethaddr which can compute the correct ethernet
85 address to use. The address can be set by ifconfig either before at
86 at the time the device is brought up. If you are using RedHat you can
87 add the line:
89 MACADDR=AA:00:04:00:03:04
91 or something similar, to /etc/sysconfig/network-scripts/ifcfg-eth0 or
92 wherever your network card's configuration lives. Setting the MAC address
93 of your ethernet card to an address starting with "hi-ord" will cause a
94 DECnet address which matches to be added to the interface (which you can
95 verify with iproute2).
97 The default device for routing can be set through the /proc filesystem
98 by setting /proc/sys/net/decnet/default_device to the
99 device you want DECnet to route packets out of when no specific route
100 is available. Usually this will be eth0, for example:
102 echo -n "eth0" >/proc/sys/net/decnet/default_device
104 If you don't set the default device, then it will default to the first
105 ethernet card which has been autoconfigured as described above. You can
106 confirm that by looking in the default_device file of course.
108 There is a list of what the other files under /proc/sys/net/decnet/ do
109 on the kernel patch web site (shown above).
111 4) Run time kernel configuration
113 This is either done through the sysctl/proc interface (see the kernel web
114 pages for details on what the various options do) or through the iproute2
115 package in the same way as IPv4/6 configuration is performed.
117 Documentation for iproute2 is included with the package, although there is
118 as yet no specific section on DECnet, most of the features apply to both
119 IP and DECnet, albeit with DECnet addresses instead of IP addresses and
120 a reduced functionality.
122 If you want to configure a DECnet router you'll need the iproute2 package
123 since its the _only_ way to add and delete routes currently. Eventually
124 there will be a routing daemon to send and receive routing messages for
125 each interface and update the kernel routing tables accordingly. The
126 routing daemon will use netfilter to listen to routing packets, and
127 rtnetlink to update the kernels routing tables.
129 The DECnet raw socket layer has been removed since it was there purely
130 for use by the routing daemon which will now use netfilter (a much cleaner
131 and more generic solution) instead.
133 5) How can I tell if its working ?
135 Here is a quick guide of what to look for in order to know if your DECnet
136 kernel subsystem is working.
138 - Is the node address set (see /proc/sys/net/decnet/node_address)
139 - Is the node of the correct type
140 (see /proc/sys/net/decnet/conf/<dev>/forwarding)
141 - Is the Ethernet MAC address of each Ethernet card set to match
142 the DECnet address. If in doubt use the dn2ethaddr utility available
143 at the ftp archive.
144 - If the previous two steps are satisfied, and the Ethernet card is up,
145 you should find that it is listed in /proc/net/decnet_dev and also
146 that it appears as a directory in /proc/sys/net/decnet/conf/. The
147 loopback device (lo) should also appear and is required to communicate
148 within a node.
149 - If you have any DECnet routers on your network, they should appear
150 in /proc/net/decnet_neigh, otherwise this file will only contain the
151 entry for the node itself (if it doesn't check to see if lo is up).
152 - If you want to send to any node which is not listed in the
153 /proc/net/decnet_neigh file, you'll need to set the default device
154 to point to an Ethernet card with connection to a router. This is
155 again done with the /proc/sys/net/decnet/default_device file.
156 - Try starting a simple server and client, like the dnping/dnmirror
157 over the loopback interface. With luck they should communicate.
158 For this step and those after, you'll need the DECnet library
159 which can be obtained from the above ftp sites as well as the
160 actual utilities themselves.
161 - If this seems to work, then try talking to a node on your local
162 network, and see if you can obtain the same results.
163 - At this point you are on your own... :-)
165 6) How to send a bug report
167 If you've found a bug and want to report it, then there are several things
168 you can do to help me work out exactly what it is that is wrong. Useful
169 information (_most_ of which _is_ _essential_) includes:
171 - What kernel version are you running ?
172 - What version of the patch are you running ?
173 - How far though the above set of tests can you get ?
174 - What is in the /proc/decnet* files and /proc/sys/net/decnet/* files ?
175 - Which services are you running ?
176 - Which client caused the problem ?
177 - How much data was being transferred ?
178 - Was the network congested ?
179 - How can the problem be reproduced ?
180 - Can you use tcpdump to get a trace ? (N.B. Most (all?) versions of
181 tcpdump don't understand how to dump DECnet properly, so including
182 the hex listing of the packet contents is _essential_, usually the -x flag.
183 You may also need to increase the length grabbed with the -s flag. The
184 -e flag also provides very useful information (ethernet MAC addresses))
186 7) MAC FAQ
188 A quick FAQ on ethernet MAC addresses to explain how Linux and DECnet
189 interact and how to get the best performance from your hardware.
191 Ethernet cards are designed to normally only pass received network frames
192 to a host computer when they are addressed to it, or to the broadcast address.
194 Linux has an interface which allows the setting of extra addresses for
195 an ethernet card to listen to. If the ethernet card supports it, the
196 filtering operation will be done in hardware, if not the extra unwanted packets
197 received will be discarded by the host computer. In the latter case,
198 significant processor time and bus bandwidth can be used up on a busy
199 network (see the NAPI documentation for a longer explanation of these
200 effects).
202 DECnet makes use of this interface to allow running DECnet on an ethernet
203 card which has already been configured using TCP/IP (presumably using the
204 built in MAC address of the card, as usual) and/or to allow multiple DECnet
205 addresses on each physical interface. If you do this, be aware that if your
206 ethernet card doesn't support perfect hashing in its MAC address filter
207 then your computer will be doing more work than required. Some cards
208 will simply set themselves into promiscuous mode in order to receive
209 packets from the DECnet specified addresses. So if you have one of these
210 cards its better to set the MAC address of the card as described above
211 to gain the best efficiency. Better still is to use a card which supports
212 NAPI as well.
215 8) Mailing list
217 If you are keen to get involved in development, or want to ask questions
218 about configuration, or even just report bugs, then there is a mailing
219 list that you can join, details are at:
221 http://sourceforge.net/mail/?group_id=4993
223 9) Legal Info
225 The Linux DECnet project team have placed their code under the GPL. The
226 software is provided "as is" and without warranty express or implied.
227 DECnet is a trademark of Compaq. This software is not a product of
228 Compaq. We acknowledge the help of people at Compaq in providing extra
229 documentation above and beyond what was previously publicly available.
231 Steve Whitehouse <SteveW@ACM.org>