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Date: Tue, 25 Feb 2003 13:12:55 -0800
From: "Martin J. Bligh" <mbligh@aracnet.com>
To: Andrea Arcangeli <andrea@suse.de>
cc: William Lee Irwin III <wli@holomorphy.com>, Andrew Morton <akpm@digeo.com>,
       linux-kernel@vger.kernel.org
Subject: Re: Minutes from Feb 21 LSE Call
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>> Because you don't set up and tear down the rmap pte-chains for every 
>> fault in / delete of any page ... it just works off the vmas.
> 
> so basically it uses the rmap that we always had since at least 2.2 for
> everything but anon mappings, right?  this is what DaveM did a few years
> back too. This makes lots of sense to me, so at least we avoid the
> duplication of rmap information, even if it won't fix the anonymous page
> overhead, but clearly it's much lower cost for everything but anonymous
> pages.

Right ... and anonymous chains are about 95% single-reference (at least for
the case I looked at), so they're direct mapped from the struct page with
no chain at all. Cuts out something like 95% of the space overhead of
pte-chains, and 65% of the time (for kernel compile -j256 on 16x system).
However, it's going to be a little more expensive to *use* the mappings, 
so we need to measure that carefully.

M.

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