ia64/linux-2.6.18-xen.hg

view Documentation/serial-console.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
children
line source
1 Linux Serial Console
3 To use a serial port as console you need to compile the support into your
4 kernel - by default it is not compiled in. For PC style serial ports
5 it's the config option next to "Standard/generic (dumb) serial support".
6 You must compile serial support into the kernel and not as a module.
8 It is possible to specify multiple devices for console output. You can
9 define a new kernel command line option to select which device(s) to
10 use for console output.
12 The format of this option is:
14 console=device,options
16 device: tty0 for the foreground virtual console
17 ttyX for any other virtual console
18 ttySx for a serial port
19 lp0 for the first parallel port
20 ttyUSB0 for the first USB serial device
22 options: depend on the driver. For the serial port this
23 defines the baudrate/parity/bits/flow control of
24 the port, in the format BBBBPNF, where BBBB is the
25 speed, P is parity (n/o/e), N is number of bits,
26 and F is flow control ('r' for RTS). Default is
27 9600n8. The maximum baudrate is 115200.
29 You can specify multiple console= options on the kernel command line.
30 Output will appear on all of them. The last device will be used when
31 you open /dev/console. So, for example:
33 console=ttyS1,9600 console=tty0
35 defines that opening /dev/console will get you the current foreground
36 virtual console, and kernel messages will appear on both the VGA
37 console and the 2nd serial port (ttyS1 or COM2) at 9600 baud.
39 Note that you can only define one console per device type (serial, video).
41 If no console device is specified, the first device found capable of
42 acting as a system console will be used. At this time, the system
43 first looks for a VGA card and then for a serial port. So if you don't
44 have a VGA card in your system the first serial port will automatically
45 become the console.
47 You will need to create a new device to use /dev/console. The official
48 /dev/console is now character device 5,1.
50 (You can also use a network device as a console. See
51 Documentation/networking/netconsole.txt for information on that.)
53 Here's an example that will use /dev/ttyS1 (COM2) as the console.
54 Replace the sample values as needed.
56 1. Create /dev/console (real console) and /dev/tty0 (master virtual
57 console):
59 cd /dev
60 rm -f console tty0
61 mknod -m 622 console c 5 1
62 mknod -m 622 tty0 c 4 0
64 2. LILO can also take input from a serial device. This is a very
65 useful option. To tell LILO to use the serial port:
66 In lilo.conf (global section):
68 serial = 1,9600n8 (ttyS1, 9600 bd, no parity, 8 bits)
70 3. Adjust to kernel flags for the new kernel,
71 again in lilo.conf (kernel section)
73 append = "console=ttyS1,9600"
75 4. Make sure a getty runs on the serial port so that you can login to
76 it once the system is done booting. This is done by adding a line
77 like this to /etc/inittab (exact syntax depends on your getty):
79 S1:23:respawn:/sbin/getty -L ttyS1 9600 vt100
81 5. Init and /etc/ioctl.save
83 Sysvinit remembers its stty settings in a file in /etc, called
84 `/etc/ioctl.save'. REMOVE THIS FILE before using the serial
85 console for the first time, because otherwise init will probably
86 set the baudrate to 38400 (baudrate of the virtual console).
88 6. /dev/console and X
89 Programs that want to do something with the virtual console usually
90 open /dev/console. If you have created the new /dev/console device,
91 and your console is NOT the virtual console some programs will fail.
92 Those are programs that want to access the VT interface, and use
93 /dev/console instead of /dev/tty0. Some of those programs are:
95 Xfree86, svgalib, gpm, SVGATextMode
97 It should be fixed in modern versions of these programs though.
99 Note that if you boot without a console= option (or with
100 console=/dev/tty0), /dev/console is the same as /dev/tty0. In that
101 case everything will still work.
103 7. Thanks
105 Thanks to Geert Uytterhoeven <geert@linux-m68k.org>
106 for porting the patches from 2.1.4x to 2.1.6x for taking care of
107 the integration of these patches into m68k, ppc and alpha.
109 Miquel van Smoorenburg <miquels@cistron.nl>, 11-Jun-2000