Re: [PATCH 4/4] memcg: get rid of percpu_charge_mutex lock

[KAMEZAWA Hiroyuki]

On Fri, 22 Jul 2011 13:20:25 +0200
Michal Hocko <mhocko@xxxxxxx> wrote:

> percpu_charge_mutex protects from multiple simultaneous per-cpu charge
> caches draining because we might end up having too many work items.
> At least this was the case until 26fe6168 (memcg: fix percpu cached
> charge draining frequency) when we introduced a more targeted draining
> for async mode.
> Now that also sync draining is targeted we can safely remove mutex
> because we will not send more work than the current number of CPUs.
> FLUSHING_CACHED_CHARGE protects from sending the same work multiple
> times and stock->nr_pages == 0 protects from pointless sending a work
> if there is obviously nothing to be done. This is of course racy but we
> can live with it as the race window is really small (we would have to
> see FLUSHING_CACHED_CHARGE cleared while nr_pages would be still
> non-zero).
> The only remaining place where we can race is synchronous mode when we
> rely on FLUSHING_CACHED_CHARGE test which might have been set by other
> drainer on the same group but we should wait in that case as well.
> 
> Signed-off-by: Michal Hocko <mhocko@xxxxxxx>

Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>


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