Good point, it should be consistent with the others. Review updated. --matt
On Wed, Jul 23, 2014 at 9:50 PM, Prakash Surya <[email protected]> wrote: > Why not prefix the variable with "zfs_" like the rest of the parameters? > > Seems reasonable otherwise, I've seen large hash lengths on the Linux > port running Lustre-ZFS MDS servers which makes use of many 512B buffers. > > -- > Cheers, Prakash > > On Wed, Jul 23, 2014 at 08:36:29PM -0700, Matthew Ahrens wrote: > > [1]https://reviews.csiden.org/r/61/ > > 5034 ARC's buf\_hash\_table is too small > > Reviewed by: George Wilson <[2][email protected]\> > > Reviewed by: Christopher Siden <[3][email protected]\> > > Original author: Matthew Ahrens > > The ARC puts all (non-anonymous) arc_buf_hdr_t's in a hash table, > which > > is > > created at system boot time. The hash table is sized such that if all > > of > > physical memory was filled with 64K blocks, the hash chain length > would > > average > > less than 1.0. However, on a system with typical block size of 8k, > > this can lead to > > long hash chain lengths. I've observed average length ~6.5; > > theoretically it > > could be up to 16 (because evicted "ghost" entries are also in the > > hashtable). > > By increasing the hash table size to have enough entries for average > > length 1.0 > > when memory is filled with 8k blocks, we can obtain a 18% performance > > improvement on cached reads. (680MB/s -> 805MB/s) > > The hash table size should also be tunable, rather than hard coded. > > --matt > > > > References > > > > 1. https://reviews.csiden.org/r/61/ > > 2. mailto:[email protected] > > 3. mailto:[email protected] > > > _______________________________________________ > > developer mailing list > > [email protected] > > http://lists.open-zfs.org/mailman/listinfo/developer > >
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