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From: Ingo Molnar <mingo@elte.hu>
To: Christoph Hellwig <hch@infradead.org>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	Andrew Morton <akpm@osdl.org>
Subject: Re: [PATCH] mm: remove global locks from mm/highmem.c
Date: Sun, 28 Jan 2007 16:17:00 +0100	[thread overview]
Message-ID: <20070128151700.GA7644@elte.hu> (raw)
In-Reply-To: <20070128144933.GD16552@infradead.org>


* Christoph Hellwig <hch@infradead.org> wrote:

> On Sun, Jan 28, 2007 at 03:11:34PM +0100, Peter Zijlstra wrote:
> > Eradicate global locks.
> > 
> >  - kmap_lock is removed by extensive use of atomic_t, a new flush
> >    scheme and modifying set_page_address to only allow NULL<->virt
> >    transitions.
> 
> What's the point for this? [...]

scalability. I did lock profiling on the -rt kernel, which exposes such 
things nicely. Half of the lock contention events during kernel compile 
were due to kmap(). (The system had 2 GB of RAM, so 40% lowmem, 60% 
highmem.)

> [...] In doubt we just need to convert that caller to kmap_atomic.

the pagecache ones cannot be converted to kmap_atomic, because we can 
block while holding them. Plus kmap_atomic is quite a bit slower than 
this scalable version of kmap().

	Ingo

ps. please fix your mailer to not emit Mail-Followup-To headers. In Mutt
    you can do this via "set followup_to=no" in your .muttrc.

  reply	other threads:[~2007-01-28 15:18 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-01-28 14:11 Peter Zijlstra
2007-01-28 14:49 ` Christoph Hellwig
2007-01-28 15:17   ` Ingo Molnar [this message]
2007-01-28 15:28     ` Christoph Hellwig
2007-01-28 15:48       ` Ingo Molnar
2007-01-28 15:54         ` Christoph Hellwig
2007-01-28 18:19           ` Ingo Molnar
2007-01-28 22:29 ` Andrew Morton
2007-01-29  2:52   ` Nick Piggin
2007-01-29  9:44   ` Peter Zijlstra
2007-01-30  1:31     ` Martin J. Bligh
2007-01-30  1:41       ` Andrew Morton
2007-01-30  1:49         ` Martin J. Bligh
2007-01-30  2:15           ` Andrew Morton
2007-01-31  0:44             ` David Chinner
2007-01-31  1:11               ` Andrew Morton
2007-01-31  3:22                 ` David Chinner
2007-02-02 12:05                   ` Christoph Hellwig
2007-02-02 19:24                     ` Matt Mackall
2007-02-02 23:16                       ` David Chinner
2007-02-02 23:14                     ` David Chinner
2007-01-29 19:08   ` Ingo Molnar
2007-01-29 19:19     ` Hugh Dickins
2007-01-29 19:53       ` Ingo Molnar
2007-01-29 20:06     ` Ingo Molnar
2007-01-30  2:02     ` Nick Piggin

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