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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 <> 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 <>

hmm..maybe good.
Reviewed-by: KAMEZAWA Hiroyuki <>

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