1 files changed, 25 insertions, 0 deletions

diff --git a/Documentation/cpusets.txt b/Documentation/cpusets.txt
index a09a8eb80665..e2d9afc30d2d 100644
--- a/Documentation/cpusets.txt
+++ b/Documentation/cpusets.txt
@@ -192,6 +192,7 @@ containing the following files describing that cpuset:
 
  - cpus: list of CPUs in that cpuset
  - mems: list of Memory Nodes in that cpuset
+ - memory_migrate flag: if set, move pages to cpusets nodes
  - cpu_exclusive flag: is cpu placement exclusive?
  - mem_exclusive flag: is memory placement exclusive?
  - tasks: list of tasks (by pid) attached to that cpuset
@@ -277,6 +278,30 @@ rewritten to the 'tasks' file of its cpuset.  This is done to avoid
 impacting the scheduler code in the kernel with a check for changes
 in a tasks processor placement.
 
+Normally, once a page is allocated (given a physical page
+of main memory) then that page stays on whatever node it
+was allocated, so long as it remains allocated, even if the
+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.
+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.
+
 There is an exception to the above.  If hotplug functionality is used
 to remove all the CPUs that are currently assigned to a cpuset,
 then the kernel will automatically update the cpus_allowed of all