Messages in this thread | ![/](/images/icornerl.gif) | | Date | Tue, 25 Feb 2003 13:12:55 -0800 | From | "Martin J. Bligh" <> | 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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