Messages in this thread | | | Date | Thu, 1 Aug 2002 21:32:44 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: large page patch |
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On Thu, 1 Aug 2002, David S. Miller wrote: > > Of course, if you can actually measure it, that would be > interesting. Naive math gives you a guess for the order of > magnitude effect, but nothing beats real numbers ;) > > The SYSV folks actually did have a buddy allocator a long time ago and > they did implement lazy coalescing because is supposedly improved > performance.
I bet that is mainly because of CPU scalability, and being able to avoid touching the buddy lists from multiple CPU's - the same reason _we_ have the per-CPU front-ends on various allocators.
I doubt it is because buddy matters past the 4MB mark. I just can't see how you can avoid the naive math which says that it should be 1/512th as common to coalesce to 4MB as it is to coalesce to 8kB.
Walking the buddy bitmaps for a few levels (ie up to order 3 or 4) is probably quite common, and it's likely to be bad from a SMP cache standpoint (touching a few bits with what must be fairly random patterns). So avoiding the buddy with a simple front-end is likely to win you something, without actually being meaningful at the MAX_ORDER point.
Linus
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