mempolicy: disallow static or relative flags for local preferred mode

MPOL_F_STATIC_NODES and MPOL_F_RELATIVE_NODES don't mean anything for
MPOL_PREFERRED policies that were created with an empty nodemask (for purely
local allocations).  They'll never be invalidated because the allowed mems of
a task changes or need to be rebound relative to a cpuset's placement.

Also fixes a bug identified by Lee Schermerhorn that disallowed empty
nodemasks to be passed to MPOL_PREFERRED to specify local allocations.  [A
different, somewhat incomplete, patch already existed in 25-rc5-mm1.]

Cc: Paul Jackson <pj@sgi.com>
Cc: Christoph Lameter <clameter@sgi.com>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
Cc: Andi Kleen <ak@suse.de>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 14 insertions, 2 deletions

diff --git a/Documentation/vm/numa_memory_policy.txt b/Documentation/vm/numa_memory_policy.txt
index 706410dfb9e5..1c7dd21623d2 100644
--- a/Documentation/vm/numa_memory_policy.txt
+++ b/Documentation/vm/numa_memory_policy.txt
@@ -205,6 +205,12 @@ Components of Memory Policies
             local allocation for a specific range of addresses--i.e. for
             VMA policies.
 
+            It is possible for the user to specify that local allocation is
+            always preferred by passing an empty nodemask with this mode.
+            If an empty nodemask is passed, the policy cannot use the
+            MPOL_F_STATIC_NODES or MPOL_F_RELATIVE_NODES flags described
+            below.
+
         MPOL_INTERLEAVED:  This mode specifies that page allocations be
         interleaved, on a page granularity, across the nodes specified in
         the policy.  This mode also behaves slightly differently, based on
@@ -254,7 +260,10 @@ Components of Memory Policies
             occurs over that node.  If no nodes from the user's nodemask are
             now allowed, the Default behavior is used.
 
-            MPOL_F_STATIC_NODES cannot be used with MPOL_F_RELATIVE_NODES.
+            MPOL_F_STATIC_NODES cannot be combined with the
+            MPOL_F_RELATIVE_NODES flag.  It also cannot be used for
+            MPOL_PREFERRED policies that were created with an empty nodemask
+            (local allocation).
 
         MPOL_F_RELATIVE_NODES:  This flag specifies that the nodemask passed
         by the user will be mapped relative to the set of the task or VMA's
@@ -301,7 +310,10 @@ Components of Memory Policies
             set of memory nodes allowed by the task's cpuset, as that may
             change over time.
 
-            MPOL_F_RELATIVE_NODES cannot be used with MPOL_F_STATIC_NODES.
+            MPOL_F_RELATIVE_NODES cannot be combined with the
+            MPOL_F_STATIC_NODES flag.  It also cannot be used for
+            MPOL_PREFERRED policies that were created with an empty nodemask
+            (local allocation).
 
 MEMORY POLICY APIs