[RFC] Bumping ufs.dirhash_maxmem to a larger value?

[Xin LI]

[Bcc'ed to -developers@, so this can be discussed in a public list]

Hi,

It seems that vfs.ufs.dirhash_maxmem is set to 2MB.  I think this value
is slightly too small for modern machines:
 - There are many applications that relies on small files.  CVS, maildir,
   etc.  For these applications a typical need of dirhash would be much
   larger than 2MB.
 - The RAM equiped with modern computers are growing fast.
 - Increasing dirhash_maxmem does not bring too much overhead on small
   systems, as the system would automatically recycle unused entities.
   If the memory was not freed in time, then it is usually because
   the system is busy accessing a zillion of small files.  Moreover,
   it is possible for the user to change the default value back to
   a smaller value if the file indexing is not their performance
   bottleneck.

My proposal is to increase the default dirhash_maxmem value to at least
32MB or 64MB.  Any objections?

Cons for this, discussed in -developer:
 - dirhash does not implements automatical mechanism to reduce memory
   usage in response to system memory pressure, and benefits mainly to
   large directories, e.g. Maildirs.

Cheers,
-- 
Xin LI <delphij frontfree net>	http://www.delphij.net/
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