linux-kernel - Re: [PATCH, RFD]: Unbreak no-mmu mmap

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Date:	Tue, 12 Jun 2007 01:04:01 +0200
From:	Bernd Schmidt <bernds_cb1@...nline.de>
To:	Mike Frysinger <vapier.adi@...il.com>
CC:	Matt Mackall <mpm@...enic.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	David Howells <dhowells@...hat.com>,
	"Wu, Bryan" <Bryan.Wu@...log.com>, Greg Ungerer <gerg@...pgear.com>
Subject: Re: [PATCH, RFD]: Unbreak no-mmu mmap

Mike Frysinger wrote:
> On 6/9/07, Matt Mackall <mpm@...enic.com> wrote:
>> On Fri, Jun 08, 2007 at 03:53:49PM +0200, Bernd Schmidt wrote:
>> > 2. It is no longer possible to get blocks smaller than a page through
>> >    mmap.  This behaviour was used by simplemalloc, which is an insane
>> >    way of implementing malloc on nommu systems and hopefully not used
>> >    by anyone anymore.
>>
>> That's worrisome. Breaking existing apps/libraries seems like a bad
>> idea.
> 
> it isnt breaking anything ... simplemalloc() will continue to execute
> in newer kernels

While that's true, it'll have an even bigger memory overhead than it
already does (simplemalloc, by trapping into the kernel and creating
vm_area/vm_list structures for every malloc call, has huge overheads in
both time and space).
I've posted this as an RFD to get a feeling for whether we can change
behaviour here - I do expect that nommu embedded systems are less
constrained by backwards compatibility considerations, but I'd like to
hear from other embedded users whether this is a change they'd welcome.


Bernd
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