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    SubjectRe: [PATCH 2/4] memcg: unify sync and async per-cpu charge cache draining
    On Thu, 21 Jul 2011 09:50:00 +0200
    Michal Hocko <mhocko@suse.cz> wrote:

    > Currently we have two ways how to drain per-CPU caches for charges.
    > drain_all_stock_sync will synchronously drain all caches while
    > drain_all_stock_async will asynchronously drain only those that refer to
    > a given memory cgroup or its subtree in hierarchy.
    > Targeted async draining has been introduced by 26fe6168 (memcg: fix
    > percpu cached charge draining frequency) to reduce the cpu workers
    > number.
    >
    > sync draining is currently triggered only from mem_cgroup_force_empty
    > which is triggered only by userspace (mem_cgroup_force_empty_write) or
    > when a cgroup is removed (mem_cgroup_pre_destroy). Although these are
    > not usually frequent operations it still makes some sense to do targeted
    > draining as well, especially if the box has many CPUs.
    >
    > This patch unifies both methods to use the single code (drain_all_stock)
    > which relies on the original async implementation and just adds
    > flush_work to wait on all caches that are still under work for the sync
    > mode.
    > We are using FLUSHING_CACHED_CHARGE bit check to prevent from waiting on
    > a work that we haven't triggered.
    > Please note that both sync and async functions are currently protected
    > by percpu_charge_mutex so we cannot race with other drainers.
    >
    > Signed-off-by: Michal Hocko <mhocko@suse.cz>

    hmm..maybe good.
    Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>




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