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Date: Wed, 5 Mar 2008 14:16:08 -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 -mm 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: 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>
Signed-off-by: Paul Jackson <pj@....com>
---
Documentation/filesystems/tmpfs.txt | 12 +++
Documentation/vm/numa_memory_policy.txt | 131 +++++++++++++++++++++++-------
2 files changed, 112 insertions(+), 31 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 +92,18 @@ 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
+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.
+
+ =static is equivalent to MPOL_F_STATIC_NODES
+ =relative is equivalent to MPOL_F_RELATIVE_NODES
+
+For example, mpol=bind=static:NodeList, is the equivalent of an
+allocation policy of MPOL_BIND | MPOL_F_STATIC_NODES.
+
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
@@ -179,7 +181,8 @@ Components of Memory Policies
on a non-shared region of the address space. However, see
MPOL_PREFERRED below.
- The Default mode does not use the optional set of nodes.
+ It is an error for the set of nodes specified for this policy to
+ be non-empty.
MPOL_BIND: This mode specifies that memory must come from the
set of nodes specified by the policy.
@@ -231,6 +234,80 @@ Components of Memory Policies
the temporary interleaved system default policy works in this
mode.
+ Linux memory policy supports the following optional mode flags:
+
+ 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 allowed
+ 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 allowed nodes, the node (Preferred) or
+ nodemask (Bind, Interleave) is remapped to the new set of
+ allowed nodes. This may result in nodes being used that were
+ previously undesired.
+
+ With this flag, if the user-specified nodes overlap with the
+ nodes allowed by the task's cpuset, then the memory policy is
+ applied to their intersection. If the two sets of nodes do not
+ overlap, the Default policy 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 allowed from the user's nodemask, the "interleave" only
+ 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_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
+ set of allowed nodes. The kernel stores the user-passed nodemask,
+ and if the allowed nodes changes, then that original nodemask will
+ be remapped relative to the new set of allowed nodes.
+
+ Without this flag (and without MPOL_F_STATIC_NODES), anytime a
+ mempolicy is rebound because of a change in the set of allowed
+ nodes, the node (Preferred) or nodemask (Bind, Interleave) is
+ remapped to the new set of allowed nodes. That remap may not
+ preserve the relative nature of the user's passed nodemask to its
+ set of allowed nodes upon successive rebinds: a nodemask of
+ 1,3,5 may be remapped to 7-9 and then to 1-3 if the set of
+ allowed nodes is restored to its original state.
+
+ With this flag, the remap is done so that the node numbers from
+ the user's passed nodemask are relative to the set of allowed
+ nodes. In other words, if nodes 0, 2, and 4 are set in the user's
+ nodemask, the policy will be effected over the first (and in the
+ Bind or Interleave case, the third and fifth) nodes in the set of
+ allowed nodes. The nodemask passed by the user represents nodes
+ relative to task or VMA's set of allowed nodes.
+
+ If the user's nodemask includes nodes that are outside the range
+ of the new set of allowed nodes (for example, node 5 is set in
+ the user's nodemask when the set of allowed nodes is only 0-3),
+ then the remap wraps around to the beginning of the nodemask and,
+ if not already set, sets the node in the mempolicy nodemask.
+
+ For example, consider a task that is attached to a cpuset with
+ mems 2-5 that sets an Interleave policy over the same set with
+ MPOL_F_RELATIVE_NODES. If the cpuset's mems change to 3-7, the
+ interleave now occurs over nodes 3,5-6. If the cpuset's mems
+ then change to 0,2-3,5, then the interleave occurs over nodes
+ 0,3,5.
+
+ Thanks to the consistent remapping, applications preparing
+ nodemasks to specify memory policies using this flag should
+ disregard their current, actual cpuset imposed memory placement
+ and prepare the nodemask as if they were always located on
+ memory nodes 0 to N-1, where N is the number of memory nodes the
+ policy is intended to manage. Let the kernel then remap to the
+ 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.
+
MEMORY POLICY APIs
Linux supports 3 system calls for controlling memory policy. These APIS
@@ -251,7 +328,9 @@ 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
@@ -303,29 +382,19 @@ MEMORY POLICIES AND CPUSETS
Memory policies work within cpusets as described above. For memory policies
that require a node or set of nodes, the nodes are restricted to the set of
nodes whose memories are allowed by the cpuset constraints. If the nodemask
-specified for the policy contains nodes that are not allowed by the cpuset, or
-the intersection of the set of nodes specified for the policy and the set of
-nodes with memory is the empty set, the policy is considered invalid
-and cannot be installed.
-
-The interaction of memory policies and cpusets can be problematic for a
-couple of reasons:
-
-1) the memory policy APIs take physical node id's as arguments. As mentioned
- above, it is illegal to specify nodes that are not allowed in the cpuset.
- The application must query the allowed nodes using the get_mempolicy()
- API with the MPOL_F_MEMS_ALLOWED flag to determine the allowed nodes and
- restrict itself to those nodes. However, the resources available to a
- cpuset can be changed by the system administrator, or a workload manager
- application, at any time. So, a task may still get errors attempting to
- specify policy nodes, and must query the allowed memories again.
-
-2) when tasks in two cpusets share access to a memory region, such as shared
- memory segments created by shmget() of mmap() with the MAP_ANONYMOUS and
- MAP_SHARED flags, and any of the tasks install shared policy on the region,
- only nodes whose memories are allowed in both cpusets may be used in the
- policies. Obtaining this information requires "stepping outside" the
- memory policy APIs to use the cpuset information and requires that one
- know in what cpusets other task might be attaching to the shared region.
- Furthermore, if the cpusets' allowed memory sets are disjoint, "local"
- allocation is the only valid policy.
+specified for the policy contains nodes that are not allowed by the cpuset and
+MPOL_F_RELATIVE_NODES is not used, the intersection of the set of nodes
+specified for the policy and the set of nodes with memory is used. If the
+result is the empty set, the policy is considered invalid and cannot be
+installed. If MPOL_F_RELATIVE_NODES is used, the policy's nodes are mapped
+onto and folded into the task's set of allowed nodes as previously described.
+
+The interaction of memory policies and cpusets can be problematic when tasks
+in two cpusets share access to a memory region, such as shared memory segments
+created by shmget() of mmap() with the MAP_ANONYMOUS and MAP_SHARED flags, and
+any of the tasks install shared policy on the region, only nodes whose
+memories are allowed in both cpusets may be used in the policies. Obtaining
+this information requires "stepping outside" the memory policy APIs to use the
+cpuset information and requires that one know in what cpusets other task might
+be attaching to the shared region. Furthermore, if the cpusets' allowed
+memory sets are disjoint, "local" allocation is the only valid policy.
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