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To: torvalds@transmeta.com (Linus Torvalds)
Cc: linux-kernel@vger.kernel.org
Subject: Re: Kernel is unstable
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From: Christoph Rohland <cr@sap.com>
Date: 02 Mar 2001 09:23:21 +0100
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Hi Linus,

On 1 Mar 2001, Linus Torvalds wrote:
> Note how do_brk() does the merging itself (see the comment "Can we
> just expand an old anonymous mapping?"), and that it's basically
> free when done that way, with no worries about locking etc. The same
> could be done fairly trivially in mmap too, but I never saw any real
> usage patterns that made it look all that worthwhile (*). Handling
> the mmap case the same way do_brk() does it would fix the behaviour
> of this pathological example too..

Oh there is at least one application, which does trigger the merging
quite often: SAP R/3. We have a big memory area which is handled in 1M
blocks which get mmaped/munmapped/mprotected all the time. This now
leads to a really big avl tree which before has been much smaller.

I am not sure that the merging is a gain since it in itself is a
overhead and we work on fixed blocks. I simply wanted to point out
that there are applications out there which trigger it.

Greetings
		Christoph

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