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Diffstat (limited to 'Documentation/cpusets.txt')
| -rw-r--r-- | Documentation/cpusets.txt | 25 |
1 files changed, 25 insertions, 0 deletions
diff --git a/Documentation/cpusets.txt b/Documentation/cpusets.txt index a09a8eb80665..e2d9afc30d2d 100644 --- a/Documentation/cpusets.txt +++ b/Documentation/cpusets.txt @@ -192,6 +192,7 @@ containing the following files describing that cpuset: - cpus: list of CPUs in that cpuset - mems: list of Memory Nodes in that cpuset + - memory_migrate flag: if set, move pages to cpusets nodes - cpu_exclusive flag: is cpu placement exclusive? - mem_exclusive flag: is memory placement exclusive? - tasks: list of tasks (by pid) attached to that cpuset @@ -277,6 +278,30 @@ rewritten to the 'tasks' file of its cpuset. This is done to avoid impacting the scheduler code in the kernel with a check for changes in a tasks processor placement. +Normally, once a page is allocated (given a physical page +of main memory) then that page stays on whatever node it +was allocated, so long as it remains allocated, even if the +cpusets memory placement policy 'mems' subsequently changes. +If the cpuset flag file 'memory_migrate' is set true, then when +tasks are attached to that cpuset, any pages that task had +allocated to it on nodes in its previous cpuset are migrated +to the tasks new cpuset. Depending on the implementation, +this migration may either be done by swapping the page out, +so that the next time the page is referenced, it will be paged +into the tasks new cpuset, usually on the node where it was +referenced, or this migration may be done by directly copying +the pages from the tasks previous cpuset to the new cpuset, +where possible to the same node, relative to the new cpuset, +as the node that held the page, relative to the old cpuset. +Also if 'memory_migrate' is set true, then if that cpusets +'mems' file is modified, pages allocated to tasks in that +cpuset, that were on nodes in the previous setting of 'mems', +will be moved to nodes in the new setting of 'mems.' Again, +depending on the implementation, this might be done by swapping, +or by direct copying. In either case, pages that were not in +the tasks prior cpuset, or in the cpusets prior 'mems' setting, +will not be moved. + There is an exception to the above. If hotplug functionality is used to remove all the CPUs that are currently assigned to a cpuset, then the kernel will automatically update the cpus_allowed of all |