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

Robin Getz
2007-06-11T21:05:56Z

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