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Subject[patch 4/4] mempolicy: update NUMA memory policy documentation
Updates Documentation/vm/numa_memory_policy.txt and
Documentation/filesystems/tmpfs.txt to describe optional mempolicy mode

Cc: Paul Jackson <>
Cc: Christoph Lameter <>
Cc: Lee Schermerhorn <>
Cc: Andi Kleen <>
Signed-off-by: David Rientjes <>
Documentation/filesystems/tmpfs.txt | 11 ++++++++
Documentation/vm/numa_memory_policy.txt | 41 +++++++++++++++++++++++++++----
2 files changed, 47 insertions(+), 5 deletions(-)

diff --git a/Documentation/filesystems/tmpfs.txt b/Documentation/filesystems/tmpfs.txt
--- a/Documentation/filesystems/tmpfs.txt
+++ b/Documentation/filesystems/tmpfs.txt
@@ -92,6 +92,17 @@ 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

+It is possible to specify a static NodeList by appending '=static' to
+the memory policy mode in the mpol= argument. This will require that
+tasks or VMA's restricted to a subset of allowed nodes are only allowed
+to effect the memory policy over those nodes. No remapping of the
+NodeList when the policy is rebound, which is the default behavior, is
+allowed when '=static' is specified. For example:
+mpol=bind=static:NodeList will only allocate from each node in
+ the NodeList without remapping the
+ NodeList if the policy is rebound
Note that trying to mount a tmpfs with an mpol option will fail if the
running kernel does not support NUMA; and will fail if its nodelist
specifies a node which is not online. If your system relies on that
diff --git a/Documentation/vm/numa_memory_policy.txt b/Documentation/vm/numa_memory_policy.txt
--- a/Documentation/vm/numa_memory_policy.txt
+++ b/Documentation/vm/numa_memory_policy.txt
@@ -135,9 +135,11 @@ most general to most specific:

Components of Memory Policies

- A Linux memory policy is a tuple consisting of a "mode" and an optional set
- of nodes. The mode determine the behavior of the policy, while the
- optional set of nodes can be viewed as the arguments to the behavior.
+ A Linux memory policy consists of a "mode", optional mode flags, and an
+ optional set of nodes. The mode determine the behavior of the policy,
+ the optional mode flags determine the behavior of the mode, and the
+ optional set of nodes can be viewed as the arguments to the policy
+ behavior.

Internally, memory policies are implemented by a reference counted
structure, struct mempolicy. Details of this structure will be discussed
@@ -145,7 +147,12 @@ Components of Memory Policies

Note: in some functions AND in the struct mempolicy itself, the mode
is called "policy". However, to avoid confusion with the policy tuple,
- this document will continue to use the term "mode".
+ this document will continue to use the term "mode". Since the mode and
+ optional mode flags are stored in the same struct mempolicy member
+ (specifically, pol->policy), you must use mpol_mode(pol->policy) to
+ access only the mode and mpol_flags(pol->policy) to access only the
+ flags. Any function with a formal of type enum mempolicy_mode only
+ refers to the mode.

Linux memory policy supports the following 4 behavioral modes:

@@ -231,6 +238,28 @@ Components of Memory Policies
the temporary interleaved system default policy works in this

+ Linux memory policy supports the following optional mode flag:
+ MPOL_F_STATIC_NODES: This flag specifies that the nodemask passed by
+ the user should not be remapped if the task or VMA's set of accessible
+ nodes changes after the memory policy has been defined.
+ Without this flag, anytime a mempolicy is rebound because of a
+ change in the set of accessible nodes, the node (Preferred) or
+ nodemask (Bind, Interleave) is remapped to the new set of
+ accessible nodes. This may result in nodes being used that were
+ previously undesired. With this flag, the policy is either
+ effected over the user's specified nodemask or the Default
+ behavior is used.
+ For example, consider a task that is attached to a cpuset with
+ mems 1-3 that sets an Interleave policy over the same set. If
+ the cpuset's mems change to 3-5, the Interleave will now occur
+ over nodes 3, 4, and 5. With this flag, however, since only
+ node 3 is accessible from the user's nodemask, the "interleave"
+ only occurs over that node. If no nodes from the user's
+ nodemask are now accessible, the Default behavior is used.

Linux supports 3 system calls for controlling memory policy. These APIS
@@ -251,7 +280,9 @@ Set [Task] Memory Policy:
Set's the calling task's "task/process memory policy" to mode
specified by the 'mode' argument and the set of nodes defined
by 'nmask'. 'nmask' points to a bit mask of node ids containing
- at least 'maxnode' ids.
+ at least 'maxnode' ids. Optional mode flags may be passed by
+ intersecting the 'mode' argument with the flag (for example:

See the set_mempolicy(2) man page for more details

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