[PATCH] Page migration documentation update

Update the documentation for page migration.

- Fix up bits and pieces in cpusets.txt

- Rework text in vm/page-migration to be clearer and reflect the final
  version of page migration in 2.6.16. Mention Andi Kleen's numactl
  package that contains user space tools for page migration via
  libnuma. Add reference to numa_maps and to the manpage in numactl.

- Add todo list for outstanding issues

Signed-off-by: Christoph Lameter <clameter@sgi.com>
Acked-by: Paul Jackson <pj@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 14 insertions, 27 deletions

diff --git a/Documentation/cpusets.txt b/Documentation/cpusets.txt
index 990998ee10b6..30c41459953c 100644
--- a/Documentation/cpusets.txt
+++ b/Documentation/cpusets.txt
@@ -4,8 +4,9 @@
 Copyright (C) 2004 BULL SA.
 Written by Simon.Derr@bull.net
 
-Portions Copyright (c) 2004 Silicon Graphics, Inc.
+Portions Copyright (c) 2004-2006 Silicon Graphics, Inc.
 Modified by Paul Jackson <pj@sgi.com>
+Modified by Christoph Lameter <clameter@sgi.com>
 
 CONTENTS:
 =========
@@ -90,7 +91,8 @@ This can be especially valuable on:
 
 These subsets, or "soft partitions" must be able to be dynamically
 adjusted, as the job mix changes, without impacting other concurrently
-executing jobs.
+executing jobs. The location of the running jobs pages may also be moved
+when the memory locations are changed.
 
 The kernel cpuset patch provides the minimum essential kernel
 mechanisms required to efficiently implement such subsets.  It
@@ -102,8 +104,8 @@ memory allocator code.
 1.3 How are cpusets implemented ?
 ---------------------------------
 
-Cpusets provide a Linux kernel (2.6.7 and above) mechanism to constrain
-which CPUs and Memory Nodes are used by a process or set of processes.
+Cpusets provide a Linux kernel mechanism to constrain which CPUs and
+Memory Nodes are used by a process or set of processes.
 
 The Linux kernel already has a pair of mechanisms to specify on which
 CPUs a task may be scheduled (sched_setaffinity) and on which Memory
@@ -371,22 +373,17 @@ cpusets memory placement policy 'mems' subsequently changes.
 If the cpuset flag file 'memory_migrate' is set true, then when
 tasks are attached to that cpuset, any pages that task had
 allocated to it on nodes in its previous cpuset are migrated
-to the tasks new cpuset.  Depending on the implementation,
-this migration may either be done by swapping the page out,
-so that the next time the page is referenced, it will be paged
-into the tasks new cpuset, usually on the node where it was
-referenced, or this migration may be done by directly copying
-the pages from the tasks previous cpuset to the new cpuset,
-where possible to the same node, relative to the new cpuset,
-as the node that held the page, relative to the old cpuset.
+to the tasks new cpuset. The relative placement of the page within
+the cpuset is preserved during these migration operations if possible.
+For example if the page was on the second valid node of the prior cpuset
+then the page will be placed on the second valid node of the new cpuset.
+
 Also if 'memory_migrate' is set true, then if that cpusets
 'mems' file is modified, pages allocated to tasks in that
 cpuset, that were on nodes in the previous setting of 'mems',
-will be moved to nodes in the new setting of 'mems.'  Again,
-depending on the implementation, this might be done by swapping,
-or by direct copying.  In either case, pages that were not in
-the tasks prior cpuset, or in the cpusets prior 'mems' setting,
-will not be moved.
+will be moved to nodes in the new setting of 'mems.'
+Pages that were not in the tasks prior cpuset, or in the cpusets
+prior 'mems' setting, will not be moved.
 
 There is an exception to the above.  If hotplug functionality is used
 to remove all the CPUs that are currently assigned to a cpuset,
@@ -434,16 +431,6 @@ and then start a subshell 'sh' in that cpuset:
   # The next line should display '/Charlie'
   cat /proc/self/cpuset
 
-In the case that a change of cpuset includes wanting to move already
-allocated memory pages, consider further the work of IWAMOTO
-Toshihiro <iwamoto@valinux.co.jp> for page remapping and memory
-hotremoval, which can be found at:
-
-  http://people.valinux.co.jp/~iwamoto/mh.html
-
-The integration of cpusets with such memory migration is not yet
-available.
-
 In the future, a C library interface to cpusets will likely be
 available.  For now, the only way to query or modify cpusets is
 via the cpuset file system, using the various cd, mkdir, echo, cat,