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-rw-r--r--Documentation/cgroups/cpusets.txt38
1 files changed, 19 insertions, 19 deletions
diff --git a/Documentation/cgroups/cpusets.txt b/Documentation/cgroups/cpusets.txt
index 4160df82b3f5..51682ab2dd1a 100644
--- a/Documentation/cgroups/cpusets.txt
+++ b/Documentation/cgroups/cpusets.txt
@@ -42,7 +42,7 @@ Nodes to a set of tasks. In this document "Memory Node" refers to
42an on-line node that contains memory. 42an on-line node that contains memory.
43 43
44Cpusets constrain the CPU and Memory placement of tasks to only 44Cpusets constrain the CPU and Memory placement of tasks to only
45the resources within a tasks current cpuset. They form a nested 45the resources within a task's current cpuset. They form a nested
46hierarchy visible in a virtual file system. These are the essential 46hierarchy visible in a virtual file system. These are the essential
47hooks, beyond what is already present, required to manage dynamic 47hooks, beyond what is already present, required to manage dynamic
48job placement on large systems. 48job placement on large systems.
@@ -53,11 +53,11 @@ Documentation/cgroups/cgroups.txt.
53Requests by a task, using the sched_setaffinity(2) system call to 53Requests by a task, using the sched_setaffinity(2) system call to
54include CPUs in its CPU affinity mask, and using the mbind(2) and 54include CPUs in its CPU affinity mask, and using the mbind(2) and
55set_mempolicy(2) system calls to include Memory Nodes in its memory 55set_mempolicy(2) system calls to include Memory Nodes in its memory
56policy, are both filtered through that tasks cpuset, filtering out any 56policy, are both filtered through that task's cpuset, filtering out any
57CPUs or Memory Nodes not in that cpuset. The scheduler will not 57CPUs or Memory Nodes not in that cpuset. The scheduler will not
58schedule a task on a CPU that is not allowed in its cpus_allowed 58schedule a task on a CPU that is not allowed in its cpus_allowed
59vector, and the kernel page allocator will not allocate a page on a 59vector, and the kernel page allocator will not allocate a page on a
60node that is not allowed in the requesting tasks mems_allowed vector. 60node that is not allowed in the requesting task's mems_allowed vector.
61 61
62User level code may create and destroy cpusets by name in the cgroup 62User level code may create and destroy cpusets by name in the cgroup
63virtual file system, manage the attributes and permissions of these 63virtual file system, manage the attributes and permissions of these
@@ -121,9 +121,9 @@ Cpusets extends these two mechanisms as follows:
121 - Each task in the system is attached to a cpuset, via a pointer 121 - Each task in the system is attached to a cpuset, via a pointer
122 in the task structure to a reference counted cgroup structure. 122 in the task structure to a reference counted cgroup structure.
123 - Calls to sched_setaffinity are filtered to just those CPUs 123 - Calls to sched_setaffinity are filtered to just those CPUs
124 allowed in that tasks cpuset. 124 allowed in that task's cpuset.
125 - Calls to mbind and set_mempolicy are filtered to just 125 - Calls to mbind and set_mempolicy are filtered to just
126 those Memory Nodes allowed in that tasks cpuset. 126 those Memory Nodes allowed in that task's cpuset.
127 - The root cpuset contains all the systems CPUs and Memory 127 - The root cpuset contains all the systems CPUs and Memory
128 Nodes. 128 Nodes.
129 - For any cpuset, one can define child cpusets containing a subset 129 - For any cpuset, one can define child cpusets containing a subset
@@ -141,11 +141,11 @@ into the rest of the kernel, none in performance critical paths:
141 - in init/main.c, to initialize the root cpuset at system boot. 141 - in init/main.c, to initialize the root cpuset at system boot.
142 - in fork and exit, to attach and detach a task from its cpuset. 142 - in fork and exit, to attach and detach a task from its cpuset.
143 - in sched_setaffinity, to mask the requested CPUs by what's 143 - in sched_setaffinity, to mask the requested CPUs by what's
144 allowed in that tasks cpuset. 144 allowed in that task's cpuset.
145 - in sched.c migrate_live_tasks(), to keep migrating tasks within 145 - in sched.c migrate_live_tasks(), to keep migrating tasks within
146 the CPUs allowed by their cpuset, if possible. 146 the CPUs allowed by their cpuset, if possible.
147 - in the mbind and set_mempolicy system calls, to mask the requested 147 - in the mbind and set_mempolicy system calls, to mask the requested
148 Memory Nodes by what's allowed in that tasks cpuset. 148 Memory Nodes by what's allowed in that task's cpuset.
149 - in page_alloc.c, to restrict memory to allowed nodes. 149 - in page_alloc.c, to restrict memory to allowed nodes.
150 - in vmscan.c, to restrict page recovery to the current cpuset. 150 - in vmscan.c, to restrict page recovery to the current cpuset.
151 151
@@ -155,7 +155,7 @@ new system calls are added for cpusets - all support for querying and
155modifying cpusets is via this cpuset file system. 155modifying cpusets is via this cpuset file system.
156 156
157The /proc/<pid>/status file for each task has four added lines, 157The /proc/<pid>/status file for each task has four added lines,
158displaying the tasks cpus_allowed (on which CPUs it may be scheduled) 158displaying the task's cpus_allowed (on which CPUs it may be scheduled)
159and mems_allowed (on which Memory Nodes it may obtain memory), 159and mems_allowed (on which Memory Nodes it may obtain memory),
160in the two formats seen in the following example: 160in the two formats seen in the following example:
161 161
@@ -323,17 +323,17 @@ stack segment pages of a task.
323 323
324By default, both kinds of memory spreading are off, and memory 324By default, both kinds of memory spreading are off, and memory
325pages are allocated on the node local to where the task is running, 325pages are allocated on the node local to where the task is running,
326except perhaps as modified by the tasks NUMA mempolicy or cpuset 326except perhaps as modified by the task's NUMA mempolicy or cpuset
327configuration, so long as sufficient free memory pages are available. 327configuration, so long as sufficient free memory pages are available.
328 328
329When new cpusets are created, they inherit the memory spread settings 329When new cpusets are created, they inherit the memory spread settings
330of their parent. 330of their parent.
331 331
332Setting memory spreading causes allocations for the affected page 332Setting memory spreading causes allocations for the affected page
333or slab caches to ignore the tasks NUMA mempolicy and be spread 333or slab caches to ignore the task's NUMA mempolicy and be spread
334instead. Tasks using mbind() or set_mempolicy() calls to set NUMA 334instead. Tasks using mbind() or set_mempolicy() calls to set NUMA
335mempolicies will not notice any change in these calls as a result of 335mempolicies will not notice any change in these calls as a result of
336their containing tasks memory spread settings. If memory spreading 336their containing task's memory spread settings. If memory spreading
337is turned off, then the currently specified NUMA mempolicy once again 337is turned off, then the currently specified NUMA mempolicy once again
338applies to memory page allocations. 338applies to memory page allocations.
339 339
@@ -357,7 +357,7 @@ pages from the node returned by cpuset_mem_spread_node().
357 357
358The cpuset_mem_spread_node() routine is also simple. It uses the 358The cpuset_mem_spread_node() routine is also simple. It uses the
359value of a per-task rotor cpuset_mem_spread_rotor to select the next 359value of a per-task rotor cpuset_mem_spread_rotor to select the next
360node in the current tasks mems_allowed to prefer for the allocation. 360node in the current task's mems_allowed to prefer for the allocation.
361 361
362This memory placement policy is also known (in other contexts) as 362This memory placement policy is also known (in other contexts) as
363round-robin or interleave. 363round-robin or interleave.
@@ -594,7 +594,7 @@ is attached, is subtle.
594If a cpuset has its Memory Nodes modified, then for each task attached 594If a cpuset has its Memory Nodes modified, then for each task attached
595to that cpuset, the next time that the kernel attempts to allocate 595to that cpuset, the next time that the kernel attempts to allocate
596a page of memory for that task, the kernel will notice the change 596a page of memory for that task, the kernel will notice the change
597in the tasks cpuset, and update its per-task memory placement to 597in the task's cpuset, and update its per-task memory placement to
598remain within the new cpusets memory placement. If the task was using 598remain within the new cpusets memory placement. If the task was using
599mempolicy MPOL_BIND, and the nodes to which it was bound overlap with 599mempolicy MPOL_BIND, and the nodes to which it was bound overlap with
600its new cpuset, then the task will continue to use whatever subset 600its new cpuset, then the task will continue to use whatever subset
@@ -603,13 +603,13 @@ was using MPOL_BIND and now none of its MPOL_BIND nodes are allowed
603in the new cpuset, then the task will be essentially treated as if it 603in the new cpuset, then the task will be essentially treated as if it
604was MPOL_BIND bound to the new cpuset (even though its NUMA placement, 604was MPOL_BIND bound to the new cpuset (even though its NUMA placement,
605as queried by get_mempolicy(), doesn't change). If a task is moved 605as queried by get_mempolicy(), doesn't change). If a task is moved
606from one cpuset to another, then the kernel will adjust the tasks 606from one cpuset to another, then the kernel will adjust the task's
607memory placement, as above, the next time that the kernel attempts 607memory placement, as above, the next time that the kernel attempts
608to allocate a page of memory for that task. 608to allocate a page of memory for that task.
609 609
610If a cpuset has its 'cpuset.cpus' modified, then each task in that cpuset 610If a cpuset has its 'cpuset.cpus' modified, then each task in that cpuset
611will have its allowed CPU placement changed immediately. Similarly, 611will have its allowed CPU placement changed immediately. Similarly,
612if a tasks pid is written to another cpusets 'cpuset.tasks' file, then its 612if a task's pid is written to another cpusets 'cpuset.tasks' file, then its
613allowed CPU placement is changed immediately. If such a task had been 613allowed CPU placement is changed immediately. If such a task had been
614bound to some subset of its cpuset using the sched_setaffinity() call, 614bound to some subset of its cpuset using the sched_setaffinity() call,
615the task will be allowed to run on any CPU allowed in its new cpuset, 615the task will be allowed to run on any CPU allowed in its new cpuset,
@@ -626,16 +626,16 @@ cpusets memory placement policy 'cpuset.mems' subsequently changes.
626If the cpuset flag file 'cpuset.memory_migrate' is set true, then when 626If the cpuset flag file 'cpuset.memory_migrate' is set true, then when
627tasks are attached to that cpuset, any pages that task had 627tasks are attached to that cpuset, any pages that task had
628allocated to it on nodes in its previous cpuset are migrated 628allocated to it on nodes in its previous cpuset are migrated
629to the tasks new cpuset. The relative placement of the page within 629to the task's new cpuset. The relative placement of the page within
630the cpuset is preserved during these migration operations if possible. 630the cpuset is preserved during these migration operations if possible.
631For example if the page was on the second valid node of the prior cpuset 631For example if the page was on the second valid node of the prior cpuset
632then the page will be placed on the second valid node of the new cpuset. 632then the page will be placed on the second valid node of the new cpuset.
633 633
634Also if 'cpuset.memory_migrate' is set true, then if that cpusets 634Also if 'cpuset.memory_migrate' is set true, then if that cpuset's
635'cpuset.mems' file is modified, pages allocated to tasks in that 635'cpuset.mems' file is modified, pages allocated to tasks in that
636cpuset, that were on nodes in the previous setting of 'cpuset.mems', 636cpuset, that were on nodes in the previous setting of 'cpuset.mems',
637will be moved to nodes in the new setting of 'mems.' 637will be moved to nodes in the new setting of 'mems.'
638Pages that were not in the tasks prior cpuset, or in the cpusets 638Pages that were not in the task's prior cpuset, or in the cpuset's
639prior 'cpuset.mems' setting, will not be moved. 639prior 'cpuset.mems' setting, will not be moved.
640 640
641There is an exception to the above. If hotplug functionality is used 641There is an exception to the above. If hotplug functionality is used
@@ -655,7 +655,7 @@ There is a second exception to the above. GFP_ATOMIC requests are
655kernel internal allocations that must be satisfied, immediately. 655kernel internal allocations that must be satisfied, immediately.
656The kernel may drop some request, in rare cases even panic, if a 656The kernel may drop some request, in rare cases even panic, if a
657GFP_ATOMIC alloc fails. If the request cannot be satisfied within 657GFP_ATOMIC alloc fails. If the request cannot be satisfied within
658the current tasks cpuset, then we relax the cpuset, and look for 658the current task's cpuset, then we relax the cpuset, and look for
659memory anywhere we can find it. It's better to violate the cpuset 659memory anywhere we can find it. It's better to violate the cpuset
660than stress the kernel. 660than stress the kernel.
661 661