On Thu, Jul 24, 2014 at 2:26 AM, Steven Hartland <[email protected]> wrote:
> Is it worth increasing the default value as well? > > I decreased the default value from 64K to 8K. What value do you think would be appropriate, and why? --matt > Steve > > ----- Original Message ----- From: "Matthew Ahrens" <[email protected]> > To: "Prakash Surya" <[email protected]> > Cc: "developer" <[email protected]>; "illumos-zfs" < > [email protected]> > Sent: Thursday, July 24, 2014 6:06 AM > Subject: Re: [OpenZFS Developer] [review request] 5034 ARC's > buf_hash_table is too small > > > > 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 >>> >>> >>> >> > > ------------------------------------------------------------ > -------------------- > > > > _______________________________________________ >> developer mailing list >> [email protected] >> http://lists.open-zfs.org/mailman/listinfo/developer >> >>
_______________________________________________ developer mailing list [email protected] http://lists.open-zfs.org/mailman/listinfo/developer
