view Documentation/ldm.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 LDM - Logical Disk Manager (Dynamic Disks)
3 ------------------------------------------
5 Overview
6 --------
8 Windows 2000 and XP use a new partitioning scheme. It is a complete
9 replacement for the MSDOS style partitions. It stores its information in a
10 1MiB journalled database at the end of the physical disk. The size of
11 partitions is limited only by disk space. The maximum number of partitions is
12 nearly 2000.
14 Any partitions created under the LDM are called "Dynamic Disks". There are no
15 longer any primary or extended partitions. Normal MSDOS style partitions are
16 now known as Basic Disks.
18 If you wish to use Spanned, Striped, Mirrored or RAID 5 Volumes, you must use
19 Dynamic Disks. The journalling allows Windows to make changes to these
20 partitions and filesystems without the need to reboot.
22 Once the LDM driver has divided up the disk, you can use the MD driver to
23 assemble any multi-partition volumes, e.g. Stripes, RAID5.
25 To prevent legacy applications from repartitioning the disk, the LDM creates a
26 dummy MSDOS partition containing one disk-sized partition.
29 Example
30 -------
32 Below we have a 50MiB disk, divided into seven partitions.
33 N.B. The missing 1MiB at the end of the disk is where the LDM database is
34 stored.
36 Device | Offset Bytes Sectors MiB | Size Bytes Sectors MiB
37 -------+----------------------------+---------------------------
38 hda | 0 0 0 | 52428800 102400 50
39 hda1 | 51380224 100352 49 | 1048576 2048 1
40 hda2 | 16384 32 0 | 6979584 13632 6
41 hda3 | 6995968 13664 6 | 10485760 20480 10
42 hda4 | 17481728 34144 16 | 4194304 8192 4
43 hda5 | 21676032 42336 20 | 5242880 10240 5
44 hda6 | 26918912 52576 25 | 10485760 20480 10
45 hda7 | 37404672 73056 35 | 13959168 27264 13
47 The LDM Database may not store the partitions in the order that they appear on
48 disk, but the driver will sort them.
50 When Linux boots, you will see something like:
52 hda: 102400 sectors w/32KiB Cache, CHS=50/64/32
53 hda: [LDM] hda1 hda2 hda3 hda4 hda5 hda6 hda7
56 Compiling LDM Support
57 ---------------------
59 To enable LDM, choose the following two options:
61 "Advanced partition selection" CONFIG_PARTITION_ADVANCED
62 "Windows Logical Disk Manager (Dynamic Disk) support" CONFIG_LDM_PARTITION
64 If you believe the driver isn't working as it should, you can enable the extra
65 debugging code. This will produce a LOT of output. The option is:
67 "Windows LDM extra logging" CONFIG_LDM_DEBUG
69 N.B. The partition code cannot be compiled as a module.
71 As with all the partition code, if the driver doesn't see signs of its type of
72 partition, it will pass control to another driver, so there is no harm in
73 enabling it.
75 If you have Dynamic Disks but don't enable the driver, then all you will see
76 is a dummy MSDOS partition filling the whole disk. You won't be able to mount
77 any of the volumes on the disk.
80 Booting
81 -------
83 If you enable LDM support, then lilo is capable of booting from any of the
84 discovered partitions. However, grub does not understand the LDM partitioning
85 and cannot boot from a Dynamic Disk.
88 More Documentation
89 ------------------
91 There is an Overview of the LDM online together with complete Technical
92 Documentation. It can also be downloaded in html.
94 http://linux-ntfs.sourceforge.net/ldm/index.html
95 http://linux-ntfs.sourceforge.net/downloads.html
97 If you have any LDM questions that aren't answered on the website, email me.
99 Cheers,
100 FlatCap - Richard Russon
101 ldm@flatcap.org