Re: malloc not behaving well when brk space is limited?

[u-igbb@aetey.se]

On Sat, Mar 29, 2014 at 01:22:12PM -0400, Rich Felker wrote:
> On Sat, Mar 29, 2014 at 07:15:02PM +0200, Timo Teras wrote:
> > musl does not support external malloc. musl internal calls to
> > malloc() are not overridable.

Ok.

> > I think you need to fix kernel. Rewrite allocator in musl. Or add the

Too bad I can not choose the kernel on all the computers where I want my
applications to run. To the contrary I am building as portable applications
as possible. Hardly this situation is out of scope of musl (?)

> > fallback code to mmap - but dalias said it's "hard". Perhaps still
> > should be still reconsidered.
> 
> Unfortunately the approach I want to use with mmap seems to be what
> glibc uses for its thread-local arenas, and it performs something like
> 2 to 10 times worse than brk... So unless we can solve that, I don't
> think it's a good option. It could be a fallback, but I still don't
> want PIE binaries running that much slower just because the kernel is
> doing something wacky and wrong.

It is a _lot_ better to run an order of magnitude slower than to fail
totally, isn't it? If you have any code doing mmap-fallback, I would be
willing to test it and hopefully use.

> We need a good solution for this problem but I don't have one yet.

This looks like a showstopper. The applications do not work properly
as-is and replacing malloc or adding mmap support from scratch by myself
is a threshold too high, given the time constraints. :(

In other words, a bad solution would be much better than no solution.

Otherwise my impression from musl until now is excellent. Thanks
for your work on it.

Regards,
Rune