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Date: Fri, 9 Nov 2001 11:05:32 +1100
From: Anton Blanchard <anton@samba.org>
To: Andi Kleen <ak@suse.de>
Cc: Ingo Molnar <mingo@elte.hu>, linux-kernel@vger.kernel.org
Subject: Re: speed difference between using hard-linked and modular drives?
Message-ID: <20011109110532.B6822@krispykreme>
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> > we should fix this by trying to allocate continuous physical memory if
> > possible, and fall back to vmalloc() only if this allocation fails.
> 
> Check -aa. A patch to do that has been in there for some time now.

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.

Anton
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