Message-ID: <4143D246.6030101@yahoo.com.au>
Date: Sun, 12 Sep 2004 14:36:22 +1000
From: Nick Piggin <nickpiggin@yahoo.com.au>
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To: William Lee Irwin III <wli@holomorphy.com>
CC: Marcelo Tosatti <marcelo.tosatti@cyclades.com>,
       Andrew Morton <akpm@osdl.org>, linux-kernel@vger.kernel.org
Subject: Re: [pagevec] resize pagevec to O(lg(NR_CPUS))
References: <20040909163929.GA4484@logos.cnet> <20040909155226.714dc704.akpm@osdl.org> <20040909230905.GO3106@holomorphy.com> <20040909162245.606403d3.akpm@osdl.org> <20040910000717.GR3106@holomorphy.com> <414133EB.8020802@yahoo.com.au> <20040910174915.GA4750@logos.cnet> <41439884.8040909@yahoo.com.au> <20040912052308.GE2660@holomorphy.com>
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William Lee Irwin III wrote:

> 
> It's unclear what you're estimating the size of. PAGEVEC_SIZE of 62

Overhead of the loaded pagevec.

[snip]

> 
> mapping->tree_lock is affected as well as zone->lru_lock. The workload
> obviously has to touch the relevant locks for pagevecs to be relevant;
> however, the primary factor in the effectiveness of pagevecs is the
> lock transfer time, which is not likely to vary significantly on boxen
> such as the OSDL STP machines. You should use a workload stressing
> mapping->tree_lock via codepaths using radix_tree_gang_lookup() and
> getting runtime on OSDL's NUMA-Q or otherwise asking SGI to test its
> effects, otherwise you're dorking around with boxen with identical
> characteristics as far as batched locking is concerned.
>

Yeah I forgot about that. I guess it probably would be easier to
get contention on the tree lock.
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