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SubjectRe: [PATCH 23/24] cfq-iosched: collect stats from dead cfqgs
On Fri, Dec 28, 2012 at 12:35:45PM -0800, Tejun Heo wrote:
> To support hierarchical stats, it's necessary to remember stats from
> dead children. Add cfqg->dead_stats and make a dying cfqg transfer
> its stats to the parent's dead-stats.
> The transfer happens form ->pd_offline_fn() and it is possible that
> there are some residual IOs completing afterwards. Currently, we lose
> these stats. Given that cgroup removal isn't a very high frequency
> operation and the amount of residual IOs on offline are likely to be
> nil or small, this shouldn't be a big deal and the complexity needed
> to handle residual IOs - another callback and rather elaborate
> synchronization to reach and lock the matching q - doesn't seem
> justified.
> Signed-off-by: Tejun Heo <>

Acked-by: Vivek Goyal <>


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