From: Neil Brown <neilb@suse.de>
Subject: Re: [PATCH 4/8] knfsd: repcache: split hash index
Date: Mon, 16 Oct 2006 20:23:30 +1000
Message-ID: <17715.23970.155314.297331@cse.unsw.edu.au>
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	<20061016095121.GB8568@sgi.com>
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Cc: Linux NFS Mailing List <nfs@lists.sourceforge.net>
To: Greg Banks <gnb@sgi.com>
In-Reply-To: message from Greg Banks on Monday October 16
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On Monday October 16, gnb@sgi.com wrote:
> 
> Let's look at the maths.  If we were to limit cache_buckets[] to a
> single page, I calculate that would give us 186 entries on ia64, 46
> on x86_64, and 68 on i386 (fewer if various spinlock-related config
> options are enabled).  That's too low on x86_64 but fine on the other
> platforms.  With a single order-1 allocation we could cover most
> bases.

I had thought that ____cacheline_aligned_in_smp would have padded it
more making few entries per page, but that probably isn't important.

> 
> Alternatively, we could allocate the buckets separately and make
> cache_buckets[] an array of pointers to buckets.  Then we could do a
> single (say) 128*sizeof(svc_cache_bucket*) allocation plus (say) 128 *
> sizeof(svc_cache_bucket) allocations, all of which would be order 0.
> Now we've effectively got a 3-level fat tree keyed on hash value.
> 
> The more I think about it, the more I like this idea.
> 

Me too.

NeilBrown

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