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

[Tulio Guimarães da Silva]

Dumb me, forgot do redirect to the list. Sorry for that.

Tulio G. Silva

-------- Original Message --------
Subject: 	Re: [RFC] Bumping ufs.dirhash_maxmem to a larger value?
Date: 	Mon, 08 Aug 2005 11:08:49 -0300
From: 	Tulio Guimarães da Silva <tuliogs at pgt.mpt.gov.br>
To: 	Xin LI <delphij at frontfree.net>
References: 	<20050807184707.GA61714 at frontfree.net> 
<42F659AE.80905 at mac.com> <20050807190533.GA61954 at frontfree.net>



  I´m suggesting this without any clue of the amount of work required, 
but it´s a suggestion, anyway: maybe it could be dinamically calculated 
based on the growth of dirhash usage AND available RAM...
  I guess 10% is a reasonable *max* value, but this could also be 
disabled with a sysctl or compile time variable, à lá MAX_USERS. Say, if 
not set, or set to zero, then it´ll be dynamically calculated. For an 
initial value, maybe 2% is enough (the same 2MB for a 128MB machine). 
Since customized kernels are very frequent, this should not be an issue.
  Of course, the ideal "max percentage" could be obtained from 
beta-testing, since it should be by default set for a generic setup. 
But, again, I´m just guessing. ;)

Tulio G. Silva

Xin LI wrote:

>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,
>  
>