Date: Sun, 21 Oct 2012 15:43:41 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Rik van Riel <riel@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>, mingo@redhat.com,
        linux-kernel@vger.kernel.org, aarcange@redhat.com,
        Michel Lespinasse <walken@google.com>
Subject: Re: [PATCH 4/2] numa, mm: Rename the PROT_NONE fault handling
 functions
Message-ID: <20121021134341.GA23820@gmail.com>
References: <20121018171821.7f1b1683@cuia.bos.redhat.com>
 <20121018172021.0b1f6e3d@cuia.bos.redhat.com>
 <1350646863.30157.13.camel@twins>
 <50815EA5.5080502@redhat.com>
 <20121019205407.GA9132@gmail.com>
 <20121021125007.GB19535@gmail.com>
 <5083F720.2030003@redhat.com>
 <20121021132921.GA23425@gmail.com>
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* Ingo Molnar <mingo@kernel.org> wrote:

> > Michel indicated that he does not use PROT_NONE for his 
> > working set estimation code, but instead checks the accessed 
> > bits in the page tables.
> 
> The pte_young() WSS method has a couple of fundamental 
> limitations:
> 
>  - it doesn't work with shared memory very well, the pte is per
>    mapping, not per page. The PROT_NONE method instruments the
>    physical page in essence.
> 
>  - it does not tell us which task touched the pte, in a
>    multi-threaded program
> 
> So like Peter I'd too expect these new WSS methods to eventually 
> be picked up for any serious WSS work.

Nevertheless lets wait and see until it actually happens - and 
meanwhile the prot_none namings are confusing.

So I've applied your patch as-is, with two more (new) usage 
sites converted as well. Will push it out after a bit of 
testing.

Thanks,

	Ingo
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