view Documentation/VGA-softcursor.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 Software cursor for VGA by Pavel Machek <pavel@atrey.karlin.mff.cuni.cz>
2 ======================= and Martin Mares <mj@atrey.karlin.mff.cuni.cz>
4 Linux now has some ability to manipulate cursor appearance. Normally, you
5 can set the size of hardware cursor (and also work around some ugly bugs in
6 those miserable Trident cards--see #define TRIDENT_GLITCH in drivers/video/
7 vgacon.c). You can now play a few new tricks: you can make your cursor look
8 like a non-blinking red block, make it inverse background of the character it's
9 over or to highlight that character and still choose whether the original
10 hardware cursor should remain visible or not. There may be other things I have
11 never thought of.
13 The cursor appearance is controlled by a "<ESC>[?1;2;3c" escape sequence
14 where 1, 2 and 3 are parameters described below. If you omit any of them,
15 they will default to zeroes.
17 Parameter 1 specifies cursor size (0=default, 1=invisible, 2=underline, ...,
18 8=full block) + 16 if you want the software cursor to be applied + 32 if you
19 want to always change the background color + 64 if you dislike having the
20 background the same as the foreground. Highlights are ignored for the last two
21 flags.
23 The second parameter selects character attribute bits you want to change
24 (by simply XORing them with the value of this parameter). On standard VGA,
25 the high four bits specify background and the low four the foreground. In both
26 groups, low three bits set color (as in normal color codes used by the console)
27 and the most significant one turns on highlight (or sometimes blinking--it
28 depends on the configuration of your VGA).
30 The third parameter consists of character attribute bits you want to set.
31 Bit setting takes place before bit toggling, so you can simply clear a bit by
32 including it in both the set mask and the toggle mask.
34 Examples:
35 =========
37 To get normal blinking underline, use: echo -e '\033[?2c'
38 To get blinking block, use: echo -e '\033[?6c'
39 To get red non-blinking block, use: echo -e '\033[?17;0;64c'