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Date: Fri, 9 Nov 2001 06:45:40 +0100
From: Andi Kleen <ak@suse.de>
To: Anton Blanchard <anton@samba.org>
Cc: Andi Kleen <ak@suse.de>, Ingo Molnar <mingo@elte.hu>,
        linux-kernel@vger.kernel.org
Subject: Re: speed difference between using hard-linked and modular drives?
Message-ID: <20011109064540.A13498@wotan.suse.de>
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In-Reply-To: <20011109110532.B6822@krispykreme>; from anton@samba.org on Fri, Nov 09, 2001 at 11:05:32AM +1100
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On Fri, Nov 09, 2001 at 11:05:32AM +1100, Anton Blanchard wrote:
> We also need a way to satisfy very large allocations for the hashes (eg
> the pagecache hash). On a 32G machine we get awful performance on the
> pagecache hash because we can only get an order 9 allocation out of
> get_free_pages:
> 
> http://samba.org/~anton/linux/pagecache/pagecache_before.png
> 
> When switching to vmalloc the hash is large enough to be useful:
> 
> http://samba.org/~anton/linux/pagecache/pagecache_after.png
> 
> As pointed out by Davem and Ingo we should try and avoid vmalloc here
> due to tlb trashing.

Sounds like you need a better hash function instead.

-Andi

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