dentry cache memory usage

[Casey Bodley <cbodley@umich.edu>]

I'm a developer at CITI working on the windows pnfs client.  We've
been looking into some optimizations for our name and attribute
caches, mainly involving the use of pools to avoid allocating memory
for each new entry.

We're looking for a sensible initial/maximum pool size.  Once the
maximum pool size is reached, we'll start scavenging the least
recently used entries.  Does the linux client impose any limits on the
size of the dentry cache?

I'm also curious what time limits you're using before expiring cached
attributes and lookups.

I suppose I'm just asking for magic numbers here, in the hope that
smart people have tested and benchmarked this stuff in the linux
client.

Thanks,
Casey