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

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Message-Id: <200706111708.28058.rgetz@blackfin.uclinux.org>
Date:	Mon, 11 Jun 2007 17:08:27 -0400
From:	Robin Getz <rgetz@...ckfin.uclinux.org>
To:	"Matt Mackall" <mpm@...enic.com>
Cc:	"Bernd Schmidt" <bernds_cb1@...nline.de>,
	"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

On Sat 9 Jun 2007 15:10, Matt Mackall pondered:
> 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 is a bad idea - but on noMMU - breaking existing apps/libraries is 
(unfortunately) a pretty common thing...
  - the standard distribution - uClinux - rebuilds all things : kernel, apps,
     libc, shell, etc which run on the target - everytime you type 'make'
 - the standard library - uClibc - has little concept of binary 
     compatibility, and has none in their years of releasing things.
     (which is OK, since everything is re-built with a simple 'make' anyway)

Plus - what Bernd talked about - uClibc's simple malloc, isn't used that often 
(at all that I am aware of), on any modern uClibc systems. The overhead of 
calling the kernel to manage memory kills performance.

As a user of the kernel in a noMMU environment - I would rather have Bernd's 
patch - which makes things closer to a MMU environment - and allows standard 
applications to work better (at all) - rather than backwards binary 
compatibility.

-Robin
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