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Message-ID: <43BF2D03.2030908@yahoo.com.au>
Date: Sat, 07 Jan 2006 13:52:51 +1100
From: Nick Piggin <nickpiggin@yahoo.com.au>
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To: Andrew Morton <akpm@osdl.org>
CC: Benjamin LaHaise <bcrl@kvack.org>, linux-kernel@vger.kernel.org,
       linux-mm@kvack.org
Subject: Re: [PATCH] use local_t for page statistics
References: <20060106215332.GH8979@kvack.org> <20060106163313.38c08e37.akpm@osdl.org>
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Andrew Morton wrote:
> Benjamin LaHaise <bcrl@kvack.org> wrote:
> 
>>The patch below converts the mm page_states counters to use local_t.  
>>mod_page_state shows up in a few profiles on x86 and x86-64 due to the 
>>disable/enable interrupts operations touching the flags register.  On 
>>both my laptop (Pentium M) and P4 test box this results in about 10 
>>additional /bin/bash -c exit 0 executions per second (P4 went from ~759/s 
>>to ~771/s).  Tested on x86 and x86-64.  Oh, also add a pgcow statistic 
>>for the number of COW page faults.
> 
> 
> Bah.  I think this is a better approach than the just-merged
> mm-page_state-opt.patch, so I should revert that patch first?
> 

No. On many load/store architectures there is no good way to do local_t,
so something like ppc32 or ia64 just uses all atomic operations for
local_t, and ppc64 uses 3 counters per-cpu thus tripling the cache
footprint.

Nick

-- 
SUSE Labs, Novell Inc.

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