[Humberto Massa] > As I said before, as far as I recall, the Debian installer suggested > me only filesystems that have O(1) [O(log n) worst case] directory > lookup. I chose reiserfs, but the installer IIRC suggested ext3 and > xfs as alternatives.
As Christoph (I think) said, Debian creates ext3 filesystems without
the dir_index flag, by default. He even mentioned that ext3 dir_index
may have a few problems remaining, so that this is a wise default.
You may of course use 'tune2fs -O dir_index /dev/whatever' to change
this, and then you'll have your O(1) lookups and opens. Requires
remounting, and I think an fsck pass.
HOWEVER
This is a very silly thing to argue about without benchmarks. Those
who care about this - yes, Thomas, I mean you - should get numbers.
Here's how:
(1) dynamicly link a hello world program to a dozen or so libraries
(2) find or create a Debian system with a few thousand /usr/lib files
(3) figure out execution time using your favorite loop technique
(4) rename /usr/lib to /usr/libexec, create a new /usr/lib, and use
'ln' (not 'ln -s' of course - symlinks of course just add *more*
lookups, in the original big directory) to repopulate /usr/lib
with just a few hundred library files and symlinks. You may wish
to give /lib similar treatment, but tread with care lest you find
yourself unable to complete the procedure. (For one thing you'll
want to do it in 'sash' or 'busybox'.)
(5) repeat your favorite loop technique
Getting a cold dentry cache before steps 3 and 5 is left as an exercise
to the poor sap with so much dedication to the Gentoo "premature
optimisations R us" ideals.
Oh yeah, for bonus points:
(6) put your original /usr/lib back where it was, then convert
libfoo.so.N symlinks to hard links. That will cut your directory
lookups in half. See if this makes any difference. If so, ponder
a new proposal taking this "optimisation" into account as well.
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