view Documentation/zorro.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 Writing Device Drivers for Zorro Devices
2 ----------------------------------------
4 Written by Geert Uytterhoeven <geert@linux-m68k.org>
5 Last revised: September 5, 2003
8 1. Introduction
9 ---------------
11 The Zorro bus is the bus used in the Amiga family of computers. Thanks to
12 AutoConfig(tm), it's 100% Plug-and-Play.
14 There are two types of Zorro busses, Zorro II and Zorro III:
16 - The Zorro II address space is 24-bit and lies within the first 16 MB of the
17 Amiga's address map.
19 - Zorro III is a 32-bit extension of Zorro II, which is backwards compatible
20 with Zorro II. The Zorro III address space lies outside the first 16 MB.
23 2. Probing for Zorro Devices
24 ----------------------------
26 Zorro devices are found by calling `zorro_find_device()', which returns a
27 pointer to the `next' Zorro device with the specified Zorro ID. A probe loop
28 for the board with Zorro ID `ZORRO_PROD_xxx' looks like:
30 struct zorro_dev *z = NULL;
32 while ((z = zorro_find_device(ZORRO_PROD_xxx, z))) {
33 if (!zorro_request_region(z->resource.start+MY_START, MY_SIZE,
34 "My explanation"))
35 ...
36 }
38 `ZORRO_WILDCARD' acts as a wildcard and finds any Zorro device. If your driver
39 supports different types of boards, you can use a construct like:
41 struct zorro_dev *z = NULL;
43 while ((z = zorro_find_device(ZORRO_WILDCARD, z))) {
44 if (z->id != ZORRO_PROD_xxx1 && z->id != ZORRO_PROD_xxx2 && ...)
45 continue;
46 if (!zorro_request_region(z->resource.start+MY_START, MY_SIZE,
47 "My explanation"))
48 ...
49 }
52 3. Zorro Resources
53 ------------------
55 Before you can access a Zorro device's registers, you have to make sure it's
56 not yet in use. This is done using the I/O memory space resource management
57 functions:
59 request_mem_region()
60 release_mem_region()
62 Shortcuts to claim the whole device's address space are provided as well:
64 zorro_request_device
65 zorro_release_device
68 4. Accessing the Zorro Address Space
69 ------------------------------------
71 The address regions in the Zorro device resources are Zorro bus address
72 regions. Due to the identity bus-physical address mapping on the Zorro bus,
73 they are CPU physical addresses as well.
75 The treatment of these regions depends on the type of Zorro space:
77 - Zorro II address space is always mapped and does not have to be mapped
78 explicitly using z_ioremap().
80 Conversion from bus/physical Zorro II addresses to kernel virtual addresses
81 and vice versa is done using:
83 virt_addr = ZTWO_VADDR(bus_addr);
84 bus_addr = ZTWO_PADDR(virt_addr);
86 - Zorro III address space must be mapped explicitly using z_ioremap() first
87 before it can be accessed:
89 virt_addr = z_ioremap(bus_addr, size);
90 ...
91 z_iounmap(virt_addr);
94 5. References
95 -------------
97 linux/include/linux/zorro.h
98 linux/include/asm-{m68k,ppc}/zorro.h
99 linux/include/linux/zorro_ids.h
100 linux/drivers/zorro
101 /proc/bus/zorro