Re: [PATCH] memcg: fix mapcount check in move charge code for anonymous page

[Hugh Dickins <hughd@google.com>]

On Tue, 6 Mar 2012, Naoya Horiguchi wrote:
> 
> IMO, ideally the charge of shared (both file and anon) pages should
> be accounted for all cgroups to which the processes mapping the pages
> belong to, where each charge is weighted by inverse number of mapcount.
> I think accounting total number of mapcount with another counter does
> not work, because the weight of charge depends on each page and the
> total count of mapcount doesn't describe the proportion among cgroups.
> But anyway, it adds more complexity and needs much work, so is not
> a short term fix.

That "ideal" complexity was considered before the current memcg approach
went in.  We elected to go with the less satisfying, but much simpler,
single-owner approach, and it does seem to have paid off.  I believe
that even those who had successfully developed a more complex approach
have since abandoned it for performance scalability reasons.

Hugh

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