linux-kernel - Re: [PATCH] mm: remove global locks from mm/highmem.c

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Date:	Tue, 30 Jan 2007 13:02:36 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Andrew Morton <akpm@...l.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm: remove global locks from mm/highmem.c

Ingo Molnar wrote:

> For every 64-bit Fedora box there's more than seven 32-bit boxes. I 
> think 32-bit is going to live with us far longer than many thought, so 
> we might as well make it work better. Both HIGHMEM and HIGHPTE is the 
> default on many distro kernels, which pushes the kmap infrastructure 
> quite a bit.

I don't think anybody would argue against numbers, but just that there
are not many big 32-bit SMPs anymore. And if Bill Irwin didn't fix the
kmap problem back then, it would be interesting to see a system and
workload where it actually is a bottleneck.

Not that I'm against any patch to improve scalability, if it doesn't
hurt single-threaded performance ;)

> the problem is that everything that was easy to migrate was migrated off 
> kmap() already - and it's exactly those hard cases that cannot be 
> converted (like the pagecache use) which is the most frequent kmap() 
> users.

Which pagecache use? file_read_actor()?

-- 
SUSE Labs, Novell Inc.
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