view Documentation/sparse.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 Copyright 2004 Linus Torvalds
2 Copyright 2004 Pavel Machek <pavel@suse.cz>
3 Copyright 2006 Bob Copeland <me@bobcopeland.com>
5 Using sparse for typechecking
6 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
8 "__bitwise" is a type attribute, so you have to do something like this:
10 typedef int __bitwise pm_request_t;
12 enum pm_request {
13 PM_SUSPEND = (__force pm_request_t) 1,
14 PM_RESUME = (__force pm_request_t) 2
15 };
17 which makes PM_SUSPEND and PM_RESUME "bitwise" integers (the "__force" is
18 there because sparse will complain about casting to/from a bitwise type,
19 but in this case we really _do_ want to force the conversion). And because
20 the enum values are all the same type, now "enum pm_request" will be that
21 type too.
23 And with gcc, all the __bitwise/__force stuff goes away, and it all ends
24 up looking just like integers to gcc.
26 Quite frankly, you don't need the enum there. The above all really just
27 boils down to one special "int __bitwise" type.
29 So the simpler way is to just do
31 typedef int __bitwise pm_request_t;
33 #define PM_SUSPEND ((__force pm_request_t) 1)
34 #define PM_RESUME ((__force pm_request_t) 2)
36 and you now have all the infrastructure needed for strict typechecking.
38 One small note: the constant integer "0" is special. You can use a
39 constant zero as a bitwise integer type without sparse ever complaining.
40 This is because "bitwise" (as the name implies) was designed for making
41 sure that bitwise types don't get mixed up (little-endian vs big-endian
42 vs cpu-endian vs whatever), and there the constant "0" really _is_
43 special.
45 Getting sparse
46 ~~~~~~~~~~~~~~
48 With git, you can just get it from
50 rsync://rsync.kernel.org/pub/scm/devel/sparse/sparse.git
52 and DaveJ has tar-balls at
54 http://www.codemonkey.org.uk/projects/git-snapshots/sparse/
57 Once you have it, just do
59 make
60 make install
62 as a regular user, and it will install sparse in your ~/bin directory.
64 Using sparse
65 ~~~~~~~~~~~~
67 Do a kernel make with "make C=1" to run sparse on all the C files that get
68 recompiled, or use "make C=2" to run sparse on the files whether they need to
69 be recompiled or not. The latter is a fast way to check the whole tree if you
70 have already built it.
72 The optional make variable CF can be used to pass arguments to sparse. The
73 build system passes -Wbitwise to sparse automatically. To perform endianness
74 checks, you may define __CHECK_ENDIAN__:
76 make C=2 CF="-D__CHECK_ENDIAN__"
78 These checks are disabled by default as they generate a host of warnings.