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

[Xin LI]

On Sun, Aug 07, 2005 at 02:57:50PM -0400, Chuck Swiger wrote:
[snip]
> On the other hand, I've got several firewall boxes with only 128MB, and 
> it's not reasonable to simply dedicate up to 64MB (half!) to dirhash 
> without paying more attention to the amount of physical memory that is 
> actually available.

Forgot to mention that dirhash_maxmem is the upper limit, not the exact
amount that dirhash must use.  If your firewall does not host zillion
of large directories then a bigger default dirhash_maxmem would
essentially a big no-op :-)

> How big should dirhash_maxmem be?  5-10% of available RAM, perhaps?

Actually this depends on how many large directories that you actively
access, not only the available RAM.  If you access only a little of
small directories, e.g. hosting a database, then dirhash won't help
much.  But with a lot of large directories having 1000+ files in most
of them, then raising the dirhash_maxmem will be a great help for
performance.

I think it would be great if we can implement a automatical "suggested
value" of dirhash during bootstrap stage, though, which can be overridden
through sysctl.conf or subsequent sysctl.

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