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Diffstat (limited to 'Documentation/cgroups/memory.txt')
| -rw-r--r-- | Documentation/cgroups/memory.txt | 56 |
1 files changed, 54 insertions, 2 deletions
diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt index b871f2552b45..e726fb0df719 100644 --- a/Documentation/cgroups/memory.txt +++ b/Documentation/cgroups/memory.txt @@ -262,10 +262,12 @@ some of the pages cached in the cgroup (page cache pages). 4.2 Task migration When a task migrates from one cgroup to another, it's charge is not -carried forward. The pages allocated from the original cgroup still +carried forward by default. The pages allocated from the original cgroup still remain charged to it, the charge is dropped when the page is freed or reclaimed. +Note: You can move charges of a task along with task migration. See 8. + 4.3 Removing a cgroup A cgroup can be removed by rmdir, but as discussed in sections 4.1 and 4.2, a @@ -414,7 +416,57 @@ NOTE1: Soft limits take effect over a long period of time, since they involve NOTE2: It is recommended to set the soft limit always below the hard limit, otherwise the hard limit will take precedence. -8. TODO +8. Move charges at task migration + +Users can move charges associated with a task along with task migration, that +is, uncharge task's pages from the old cgroup and charge them to the new cgroup. + +8.1 Interface + +This feature is disabled by default. It can be enabled(and disabled again) by +writing to memory.move_charge_at_immigrate of the destination cgroup. + +If you want to enable it: + +# echo (some positive value) > memory.move_charge_at_immigrate + +Note: Each bits of move_charge_at_immigrate has its own meaning about what type + of charges should be moved. See 8.2 for details. +Note: Charges are moved only when you move mm->owner, IOW, a leader of a thread + group. +Note: If we cannot find enough space for the task in the destination cgroup, we + try to make space by reclaiming memory. Task migration may fail if we + cannot make enough space. +Note: It can take several seconds if you move charges in giga bytes order. + +And if you want disable it again: + +# echo 0 > memory.move_charge_at_immigrate + +8.2 Type of charges which can be move + +Each bits of move_charge_at_immigrate has its own meaning about what type of +charges should be moved. + + bit | what type of charges would be moved ? + -----+------------------------------------------------------------------------ + 0 | A charge of an anonymous page(or swap of it) used by the target task. + | Those pages and swaps must be used only by the target task. You must + | enable Swap Extension(see 2.4) to enable move of swap charges. + +Note: Those pages and swaps must be charged to the old cgroup. +Note: More type of pages(e.g. file cache, shmem,) will be supported by other + bits in future. + +8.3 TODO + +- Add support for other types of pages(e.g. file cache, shmem, etc.). +- Implement madvise(2) to let users decide the vma to be moved or not to be + moved. +- All of moving charge operations are done under cgroup_mutex. It's not good + behavior to hold the mutex too long, so we may need some trick. + +9. TODO 1. Add support for accounting huge pages (as a separate controller) 2. Make per-cgroup scanner reclaim not-shared pages first |