Messages in this thread | | | Date | Thu, 12 Aug 1999 10:47:27 +0200 | From | Jamie Lokier <> | Subject | Re: clustering page-ins |
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Dr. Michael Weller wrote: > [madvise] > I was told somehow the origins of this function might be BSD, so it might > be worthwhile to support. I saw it in many unixes but it is usually > documented to have no effect at all.
My vote is forget madvise() until we've seen how well the kernel performs with Chuck's patches. MADV_DONTNEED may well come in handy, but I'm skeptical about MADV_SEQUENTIAL/MADV_RANDOM.
The read-ahead and clustering mechanism should notice random vs. sequential very easily, and because the kernel can deduce how fast the disk is relative to the app., it can tune the windows sizes optimally as well.
For that sort of self-tuning algorithm we've been discussing, madvise(MADV_SEQUENTIAL) makes no difference to the paging algorithm: you have to track faults in order to discover the tuning parameters anyway. And the app can't provide that info statically because it doesn't know how fast the disk/network is.
Which gives me a thought. Is there's an algorithm to discover the optimal random-access readaround cluster size, analogous to the sequential readahead window algorithm?
-- Jamie
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