Re: TASK_UNMAPPED_BASE & stack location

[Andi Kleen <ak@muc.de>]

"Martin J. Bligh" <mbligh@aracnet.com> writes:

>>> Is there any good reason we can't remove TASK_UNMAPPED_BASE, and just
>>> shove libraries directly above the program text? Red Hat seems to have
>>> patches to dynamically tune it on a per-processes basis anyway ...
>> 
>> Yes. You won't get a continuous sbrk/brk heap then anymore. Not sure it
>> is a  big problem though.
>
> Me no understand. I think this *makes* it a contiguous space. The way I see
> it, we currently allocate from TASK_UNMAPPED_BASE up to the top, then start
> again above program text. Which seems a bit silly.

The space for brk is not completely continuous anymore, especially
when you use mmap() too.

Same with mmap.

Basically mmap() and brk/sbrk (=malloc) will fragment each other.

wli's suggestion of making it a personality makes sense.

> I've moved PAGE_OFFSET around a lot (which moves the stack, as you say). 
> Haven't seen it break anything yet ... IMHO it was broken anyway if this
> hurts it. Obviously not something one could do in a stable kernel series,
> but 2.5 seems like a perfect time for it to me ... unless I'm missing some
> glibc / linker thing, it seems like a simple change.

It at least broke Sun Java.

-Andi