Using filename-hash as part of key

[Oleg Drokin <green@namesys.com>]

Hello!

   We had a discussion with Hans on read performance now.
   As everybody probably already knows, reiserfs (v3 and v4) is 
   very sensitive to order in which you write files to it if you
   want to read these files back quick. (actually this issue is the same
   with anything that uses filename hashes to quickly navigate through
   directories). In order to achieve best results you need to write
   files in the same order as hashes of their names would appear in directory.
   We refer to this order as "read optimised" ;)
   Of course writing files in read-optimised order is not always possible,
   so the idea is to use hash of file name as part of the key.
   That would allow us to allocate blocks for files in right order (only
   true for reiesr4 where we have delayed allocation).

   Obvious disadvantages are: larger keys mean more fs overhead,
   this optimisation won't work if file gets renamed later, if this directory
   is never read in sequentional order.

   But as Hans argues, usually these sequentional-read operations are ones most
   noticed because they are usually performed by humans:
   ls, tar, copy of a directory and this kind of stuff.

   Now let's listen to all the different opinions on this plan, your comments
   are welcome.

Bye,
    Oleg