On 2014/2/14 4:28, Tejun Heo wrote: > Hello, > > This is v2 of update-task-migration-path patchset. Changes from v1[L] > are > > * Rebased on top of "[PATCH cgroup/for-3.14-fixes] cgroup: update > cgroup_enable_task_cg_lists() to grab siglock" > > * 0005-cgroup-update-how-a-newly-forked-task-gets-associate.patch and > 0006-cgroup-drop-task_lock-protection-around-task-cgroups.patch > added to address the race between migration and fork paths. > > Currently, when migrating a task or process from one cgroup to > another, a flex_array is used to keep track of the target tasks and > associated css_sets. The current implementation has several issues. > > * flex_array size is limited. Given the current data structure, the > limit is ~87k on 64bit, which is pretty high but not impossible to > hit. > > * If multiple targets are being migrated, as migrating each target > involves memory allocation, it can fail at any point. cgroup core > doesn't keep track of enough state to roll back partial migration > either, so it ends up aborting with some targets migrated with no > way of finding out which. While this isn't a big issue now, we're > gonna be making more use of multi-target migration. > > * Fork path could race against migration path and it was impossible to > implement a mechanism to migrate all tasks of a cgroup to another > because migration path can't tell whether there are just forked > tasks pointing to the css_set but not linked yet. > > This patchset updates task migration path such that > > * task->cg_list and css_sets are also used to keep track of targets > during migration so that no extra memory allocation is necessary to > keep track of migration targets. > > * Migration is split into several stages so that all preparations > which may fail can be performed for all targets before actually > starting migrating tasks. Ignoring ->can_attach() failure, this can > guarantee all-or-nothing semantics of multi-target migration. > > * Newly forked tasks are now atomically associated with and linked to > the parent's css_set in cgroup_post_fork(). This guarantees that > the new task either is visible in the source cgroup once the > parent's migration is complete or ends up in the target cgroup in > the first place. This means that just keeping moving tasks out of a > cgroup until it's empty is guaranteed to migrate all tasks. > > This patchset contains the following seven patches. > > 0001-cgroup-add-css_set-mg_tasks.patch > 0002-cgroup-use-css_set-mg_tasks-to-track-target-tasks-du.patch > 0003-cgroup-separate-out-cset_group_from_root-from-task_c.patch > 0004-cgroup-split-process-task-migration-into-four-steps.patch > 0005-cgroup-update-how-a-newly-forked-task-gets-associate.patch > 0006-cgroup-drop-task_lock-protection-around-task-cgroups.patch > 0007-cgroup-update-cgroup_transfer_tasks-to-either-succee.patch > Acked-by: Li Zefan <lizefan@xxxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
