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Message-ID: <alpine.DEB.1.00.0802250016380.12368@chino.kir.corp.google.com>
Date: Mon, 25 Feb 2008 07:35:12 -0800 (PST)
From: David Rientjes <rientjes@...gle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
cc: Paul Jackson <pj@....com>, Christoph Lameter <clameter@....com>,
Lee Schermerhorn <Lee.Schermerhorn@...com>,
Andi Kleen <ak@...e.de>,
Randy Dunlap <randy.dunlap@...cle.com>,
linux-kernel@...r.kernel.org
Subject: [patch 6/6] mempolicy: update NUMA memory policy documentation
Updates Documentation/vm/numa_memory_policy.txt and
Documentation/filesystems/tmpfs.txt to describe optional mempolicy mode
flags.
Cc: Paul Jackson <pj@....com>
Cc: Christoph Lameter <clameter@....com>
Cc: Lee Schermerhorn <Lee.Schermerhorn@...com>
Cc: Andi Kleen <ak@...e.de>
Cc: Randy Dunlap <randy.dunlap@...cle.com>
Signed-off-by: David Rientjes <rientjes@...gle.com>
---
Documentation/filesystems/tmpfs.txt | 19 +++++++++++
Documentation/vm/numa_memory_policy.txt | 54 ++++++++++++++++++++++++++++--
2 files changed, 69 insertions(+), 4 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 +92,25 @@ 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
+
+It is also possible is to specify a relative NodeList by appending
+'=relative' to the memory policy mode in the mpol= argument. When the
+allowed nodes of a task or VMA changes, the mempolicy nodemask is
+rebound to maintain the same context as the previously bound nodemask.
+For example, consider a relative mempolicy nodemask of 1-3 for a task
+that is allowed access to nodes 0-4. If those permissions change to
+allow access to 3-7 instead, the mempolicy nodemask becomes 4-6.
+
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 determines 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
@@ -231,6 +233,48 @@ Components of Memory Policies
the temporary interleaved system default policy works in this
mode.
+ 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.
+
+ MPOL_F_RELATIVE_NODES: This flag specifies that the nodemask passed
+ by the user should remain in the same context as it is for the
+ current task or VMA's set of accessible nodes after the memory
+ policy has been defined.
+
+ Without this flag (and without MPOL_F_STATIC_NODES), 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.
+ With this flag, the remap is done to ensure the context of the
+ previous nodemask with its set of allowed mems is preserved.
+
+ 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 3-7, the Interleave will now occur
+ over nodes 3, 4, and 5. With this flag, however, since a
+ nodemask of 1-3 represents the contextually second, third, and
+ fourth nodes of the allowed mems, the Interleave now occurs
+ over nodes 4-6.
+
MEMORY POLICY APIs
Linux supports 3 system calls for controlling memory policy. These APIS
@@ -251,7 +295,9 @@ 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
+ combining the 'mode' argument with the flag (for example:
+ MPOL_INTERLEAVE | MPOL_F_STATIC_NODES).
See the set_mempolicy(2) man page for more details
--
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