Messages in this thread | | | Date | Fri, 04 Apr 2003 18:13:52 -0800 | From | "Martin J. Bligh" <> | Subject | Re: objrmap and vmtruncate |
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> Perhaps it is useful to itemise the prblems which we're trying to solve here: > > - ZONE_NORMAL consumption by pte_chains > > Solved by objrmap and presumably page clustering. > > - ZONE_NORMAL consumption by VMAs > > Solved by remap_file_pages. Neither objrmap nor page clustering will > help here.
I'm not convinced that we can't do something with nonlinear mappings for this ... we just need to keep a list of linear areas within the nonlinear vmas, and use that to do the objrmap stuff with. Dave and I talked about this yesterday ... we both had different terminology, but I think the same underlying fundamental concept ... I was calling them "sub-vmas" for each linear region within the nonlinear space.
The fundamental problem I came to (and I think Dave had the same problem) is that I couldn't see what problem remap_file_pages was trying to solve, so it was tricky to see if we'd cause the same thing or not. sub-vmas could certainly be a lot smaller, but we weren't thinking of 128K of the damned things, so ... the other thing is of course the setup and teardown time ... but the could be a btree or something for the structure.
Of course, if we did this, it would get rid of the whole conversion to and from object based stuff ;-) I think Dave had some other bright idea on this too, but I don't recall what it was ;-(
> - pte_chain setup and teardown CPU cost. > > objrmap does not seem to help. Page clustering might, but is unlikely to > be enabled on the machines which actually care about the overhead.
eh? Not sure what you mean by that. It helped massively ... diffprofile from kernbench showed:
-4666 -74.9% page_add_rmap -10666 -92.0% page_remove_rmap
I'd say that about an 85% reduction in cost is pretty damned fine ;-) And that was about a 20% overall reduction in the system time for the test too ... that was all for partial objrmap (file backed, not anon).
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