view Documentation/dcdbas.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 Overview
3 The Dell Systems Management Base Driver provides a sysfs interface for
4 systems management software such as Dell OpenManage to perform system
5 management interrupts and host control actions (system power cycle or
6 power off after OS shutdown) on certain Dell systems.
8 Dell OpenManage requires this driver on the following Dell PowerEdge systems:
9 300, 1300, 1400, 400SC, 500SC, 1500SC, 1550, 600SC, 1600SC, 650, 1655MC,
10 700, and 750. Other Dell software such as the open source libsmbios project
11 is expected to make use of this driver, and it may include the use of this
12 driver on other Dell systems.
14 The Dell libsmbios project aims towards providing access to as much BIOS
15 information as possible. See http://linux.dell.com/libsmbios/main/ for
16 more information about the libsmbios project.
19 System Management Interrupt
21 On some Dell systems, systems management software must access certain
22 management information via a system management interrupt (SMI). The SMI data
23 buffer must reside in 32-bit address space, and the physical address of the
24 buffer is required for the SMI. The driver maintains the memory required for
25 the SMI and provides a way for the application to generate the SMI.
26 The driver creates the following sysfs entries for systems management
27 software to perform these system management interrupts:
29 /sys/devices/platform/dcdbas/smi_data
30 /sys/devices/platform/dcdbas/smi_data_buf_phys_addr
31 /sys/devices/platform/dcdbas/smi_data_buf_size
32 /sys/devices/platform/dcdbas/smi_request
34 Systems management software must perform the following steps to execute
35 a SMI using this driver:
37 1) Lock smi_data.
38 2) Write system management command to smi_data.
39 3) Write "1" to smi_request to generate a calling interface SMI or
40 "2" to generate a raw SMI.
41 4) Read system management command response from smi_data.
42 5) Unlock smi_data.
45 Host Control Action
47 Dell OpenManage supports a host control feature that allows the administrator
48 to perform a power cycle or power off of the system after the OS has finished
49 shutting down. On some Dell systems, this host control feature requires that
50 a driver perform a SMI after the OS has finished shutting down.
52 The driver creates the following sysfs entries for systems management software
53 to schedule the driver to perform a power cycle or power off host control
54 action after the system has finished shutting down:
56 /sys/devices/platform/dcdbas/host_control_action
57 /sys/devices/platform/dcdbas/host_control_smi_type
58 /sys/devices/platform/dcdbas/host_control_on_shutdown
60 Dell OpenManage performs the following steps to execute a power cycle or
61 power off host control action using this driver:
63 1) Write host control action to be performed to host_control_action.
64 2) Write type of SMI that driver needs to perform to host_control_smi_type.
65 3) Write "1" to host_control_on_shutdown to enable host control action.
66 4) Initiate OS shutdown.
67 (Driver will perform host control SMI when it is notified that the OS
68 has finished shutting down.)
71 Host Control SMI Type
73 The following table shows the value to write to host_control_smi_type to
74 perform a power cycle or power off host control action:
76 PowerEdge System Host Control SMI Type
77 ---------------- ---------------------