Lines Matching full:policy
2 NUMA Memory Policy
5 What is NUMA Memory Policy?
8 In the Linux kernel, "memory policy" determines from which node the kernel will
11 The current memory policy support was added to Linux 2.6 around May 2004. This
12 document attempts to describe the concepts and APIs of the 2.6 memory policy
24 Memory Policy Concepts
30 The Linux kernel supports _scopes_ of memory policy, described here from
33 System Default Policy
34 this policy is "hard coded" into the kernel. It is the policy
36 one of the more specific policy scopes discussed below. When
37 the system is "up and running", the system default policy will
39 up, the system default policy will be set to interleave
44 Task/Process Policy
45 this is an optional, per-task policy. When defined for a
46 specific task, this policy controls all page allocations made
48 specific scope. If a task does not define a task policy, then
50 task policy "fall back" to the System Default Policy.
52 The task policy applies to the entire address space of a task. Thus,
55 to establish the task policy for a child task exec()'d from an
56 executable image that has no awareness of memory policy. See the
57 :ref:`Memory Policy APIs <memory_policy_apis>` section,
59 that a task may use to set/change its task/process policy.
62 [Linux kernel task] that installs the policy and any threads
64 at the time a new task policy is installed retain their current
65 policy.
67 A task policy applies only to pages allocated after the policy is
69 changes its task policy remain where they were allocated based on
70 the policy at the time they were allocated.
74 VMA Policy
76 virtual address space. A task may define a specific policy for a range
78 :ref:`Memory Policy APIs <memory_policy_apis>` section,
80 policy.
82 A VMA policy will govern the allocation of pages that back
84 address space that don't have an explicit VMA policy will fall
85 back to the task policy, which may itself fall back to the
86 System Default Policy.
90 * VMA policy applies ONLY to anonymous pages. These include
93 mmap()ed with the MAP_ANONYMOUS flag. If a VMA policy is
96 MAP_PRIVATE flag, the VMA policy will only be applied when
102 the policy is installed; and they are inherited across
109 * A task may install a new VMA policy on a sub-range of a
112 its own policy.
114 * By default, VMA policy applies only to pages allocated after
115 the policy is installed. Any pages already faulted into the
117 policy at the time they were allocated. However, since
120 installed policy.
122 Shared Policy
131 the object share the policy, and all pages allocated for the
132 shared object, by any task, will obey the shared policy.
135 mmap(MAP_ANONYMOUS|MAP_SHARED), support shared policy. When shared
136 policy support was added to Linux, the associated data structures were
139 shmem segments were never "hooked up" to the shared policy support.
141 for shared policy has not been completed.
145 with MAP_SHARED ignore any VMA policy installed on the virtual
149 task policy, if any, else System Default Policy.
151 The shared policy infrastructure supports different policies on subset
153 the task that installs the policy for each range of distinct policy.
157 a shared memory region, when one task has installed shared policy on
163 A NUMA memory policy consists of a "mode", optional mode flags, and
165 policy, the optional mode flags determine the behavior of the mode,
167 policy behavior.
173 NUMA memory policy supports the following 4 behavioral modes:
176 This mode is only used in the memory policy APIs. Internally,
177 MPOL_DEFAULT is converted to the NULL memory policy in all
178 policy scopes. Any existing non-default policy will simply be
180 MPOL_DEFAULT means "fall back to the next most specific policy
183 For example, a NULL or default task policy will fall back to the
184 system default policy. A NULL or default vma policy will fall
185 back to the task policy.
187 When specified in one of the memory policy APIs, the Default mode
190 It is an error for the set of nodes specified for this policy to
195 nodes specified by the policy. Memory will be allocated from
201 from the single node specified in the policy. If that
206 Internally, the Preferred policy uses a single node--the
209 and the policy is interpreted as local allocation. "Local"
210 allocation policy can be viewed as a Preferred policy that
216 mode. If an empty nodemask is passed, the policy cannot use
222 page granularity, across the nodes specified in the policy.
228 policy using the page offset of the faulting address into the
230 nodes specified by the policy. It then attempts to allocate a
232 specified by a Preferred policy or had been selected by a
237 the set of nodes specified by the policy using a node counter
241 specified by the policy based on the order in which they are
244 interleaved system default policy works in this mode.
248 satisfied from the nodemask specified in the policy. If there is
262 NUMA memory policy supports the following optional mode flags:
267 nodes changes after the memory policy has been defined.
276 nodes allowed by the task's cpuset, then the memory policy is
278 overlap, the Default policy is used.
281 mems 1-3 that sets an Interleave policy over the same set. If
312 nodemask, the policy will be effected over the first (and in the
324 mems 2-5 that sets an Interleave policy over the same set with
335 policy is intended to manage. Let the kernel then remap to the
344 Memory Policy Reference Counting
353 When a new memory policy is allocated, its reference count is initialized
355 new policy. When a pointer to a memory policy structure is stored in another
357 on completion of the policy installation.
359 During run-time "usage" of the policy, we attempt to minimize atomic operations
363 1) querying of the policy, either by the task itself [using the get_mempolicy()
367 2) examination of the policy to determine the policy mode and associated node
371 BIND policy nodemask is used, by reference, to filter ineligible nodes.
376 1) we never need to get/free the system default policy as this is never
379 2) for querying the policy, we do not need to take an extra reference on the
380 target task's task policy nor vma policies because we always acquire the
384 of a task or thread freeing a policy while another task or thread is
387 3) Page allocation usage of task or vma policy occurs in the fault path where
389 policy requires that the mmap_lock be held for write, the policy can't be
393 shared memory policy while another task, with a distinct mmap_lock, is
394 querying or allocating a page based on the policy. To resolve this
395 potential race, the shared policy infrastructure adds an extra reference
396 to the shared policy during lookup while holding a spin lock on the shared
397 policy management structure. This requires that we drop this extra
398 reference when we're finished "using" the policy. We must drop the
409 falling back to task or system default policy for shared memory regions,
415 Memory Policy APIs
418 Linux supports 4 system calls for controlling memory policy. These APIS
429 Set [Task] Memory Policy::
434 Set's the calling task's "task/process memory policy" to mode
444 Get [Task] Memory Policy or Related Information::
450 Queries the "task/process memory policy" of the calling task, or the
451 policy or location of a specified virtual address, depending on the
457 Install VMA/Shared Policy for a Range of Task's Address Space::
463 mbind() installs the policy specified by (mode, nmask, maxnodes) as a
464 VMA policy for the range of the calling task's address space specified
476 sys_set_mempolicy_home_node set the home node for a VMA policy present in the
480 the default allocation policy to allocate memory close to the local node for an
484 Memory Policy Command Line Interface
487 Although not strictly part of the Linux implementation of memory policy,
490 + set the task policy for a specified program via set_mempolicy(2), fork(2) and
493 + set the shared policy for a shared memory segment via mbind(2)
496 containing the memory policy system call wrappers. Some distributions
508 specified for the policy contains nodes that are not allowed by the cpuset and
510 specified for the policy and the set of nodes with memory is used. If the
511 result is the empty set, the policy is considered invalid and cannot be
512 installed. If MPOL_F_RELATIVE_NODES is used, the policy's nodes are mapped
518 any of the tasks install shared policy on the region, only nodes whose
520 this information requires "stepping outside" the memory policy APIs to use the
523 memory sets are disjoint, "local" allocation is the only valid policy.