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

From: Xin LI (delphij_at_frontfree.net)
Date: 08/07/05

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    Date: Mon, 8 Aug 2005 03:05:33 +0800
To: Chuck Swiger <cswiger@mac.com>

    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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