Re: [patch] mm: memcontrol: avoid charge statistics churn during page migration

[Johannes Weiner]

On Tue, Aug 05, 2014 at 02:24:34PM +0200, Michal Hocko wrote:
> On Mon 04-08-14 16:34:29, Johannes Weiner wrote:
> > Charge migration currently disables IRQs twice to update the charge
> > statistics for the old page and then again for the new page.
> > 
> > But migration is a seemless transition of a charge from one physical
> > page to another one of the same size, so this should be a non-event
> > from an accounting point of view.  Leave the statistics alone.
> 
> Moving stats to mem_cgroup_commit_charge sounds logical to me but does
> this work properly even for the fuse replace page cache case when old
> and new pages can already live in different memcgs?

We don't migrate if the new page is already charged.
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