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freebsd/sys/ufs
David Malone 527f5ce021 Two minor changes to dirhash, which result in some marginal benchmark
improvements.

1) If deleting an entry results in a chain of deleted slots ending in an
   empty slot, then we can be a bit more aggressive about marking slots as
   empty.

2) The last stage of the FNV hash is to xor the last byte of data
   into the hash. This means that filenames which differ only in
   the last byte will be placed close to one another in the hash
   table, which forms longer chains. To work around this common
   case, we also hash in the address of the dirhash structure.

     news/cancel = news/articles/control/cancel for a tradspool inn server
     squid2 = squid level 2 directory (dirs called 00->FF)
     squid3 = squid level 3 directory (files called 00001F00->00001FFF)

                             mean #probes for
                  home dir  mh inbox  news/cancel  tmp    squid2  squid3
old   successful  1.02      3.19      4.07         1.10    7.85   2.06
new   successful  1.04      1.32      1.27         1.04    1.93   1.17

old unsuccessful  1.08      4.50      5.37         1.17   10.76   2.69
new unsuccessful  1.08      1.73      1.64         1.17    2.89   1.37

Reviewed by:	iedowse
MFC after:	2 weeks
2002-03-20 17:58:02 +00:00
..
ffs Remove __P. 2002-03-19 22:40:48 +00:00
ifs Remove references to vm_zone.h and switch over to the new uma API. 2002-03-20 08:48:07 +00:00
ufs Two minor changes to dirhash, which result in some marginal benchmark 2002-03-20 17:58:02 +00:00