mempolicy: document cpuset interaction with tmpfs mpol mount option

Update Documentation/filesystems/tmpfs.txt to describe the interaction of
tmpfs mount option memory policy with tasks' cpuset mems_allowed.

Note: the mount(8) man page [in the util-linux-ng package] requires
similiar updates.

Signed-off-by: Lee Schermerhorn <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Ravikiran Thirumalai <[email protected]>
Cc: KOSAKI Motohiro <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: David Rientjes <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 9 insertions, 1 deletions

diff --git a/Documentation/filesystems/tmpfs.txt b/Documentation/filesystems/tmpfs.txt
index fe09a2cb1858..98ef55124158 100644
--- a/Documentation/filesystems/tmpfs.txt
+++ b/Documentation/filesystems/tmpfs.txt
@@ -94,11 +94,19 @@ NodeList format is a comma-separated list of decimal numbers and ranges,
 a range being two hyphen-separated decimal numbers, the smallest and
 largest node numbers in the range.  For example, mpol=bind:0-3,5,7,9-15
 
+A memory policy with a valid NodeList will be saved, as specified, for
+use at file creation time.  When a task allocates a file in the file
+system, the mount option memory policy will be applied with a NodeList,
+if any, modified by the calling task's cpuset constraints
+[See Documentation/cgroups/cpusets.txt] and any optional flags, listed
+below.  If the resulting NodeLists is the empty set, the effective memory
+policy for the file will revert to "default" policy.
+
 NUMA memory allocation policies have optional flags that can be used in
 conjunction with their modes.  These optional flags can be specified
 when tmpfs is mounted by appending them to the mode before the NodeList.
 See Documentation/vm/numa_memory_policy.txt for a list of all available
-memory allocation policy mode flags.
+memory allocation policy mode flags and their effect on memory policy.
 
 	=static		is equivalent to	MPOL_F_STATIC_NODES
 	=relative	is equivalent to	MPOL_F_RELATIVE_NODES