Messages in this thread | | | Date | Mon, 7 Aug 2000 10:55:58 -0700 (PDT) | From | Matthew Dillon <> | Subject | Re: RFC: design for new VM |
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:> if 300 processes fault on the same backing file offset you are going :> to hit a bottleneck with MP locking anyway, just at a deeper level :> (the filesystem rather then the VM system). : :Erm... I'm not sure about that - for one thing, you are not caching :results of bmap(). We do. And our VFS is BKL-free, so contention really :hits only on the VOP_BALLOC() level (that can be fixed too, but that's :another story).
Well... actually, a side effect of the FreeBSD buffer cache is to cache BMAP translations.
What we do do, which kinda kills the cacheability aspects of balloc in some cases, is VOP_REALLOC() -- that is, the FFS filesystem will reallocate blocks to implement on-the-fly defragmentation. This typically occurs on writes. It works *very* well. This is a feature that actually used to be in FFS a few years ago but had to be turned off due to bugs. The bugs were fixed about a year ago and realloc was turned on by default in 4.x.
-Matt Matthew Dillon <dillon@backplane.com>
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