Re: Dumper problems and a possible solutions

[Samuel Bronson <naesten@gmail.com>]

On 6/25/14, Rich Felker <dalias@libc.org> wrote:

> In musl's malloc, we use brk if it's available (note: with PIE, most
> kernels give you almost no available brk space due to the way the
> mappings are laid out) [...]

Yeah, that tiny gap has bitten in other ways, too:
<http://www.postgresql.org/message-id/20140519115318.GB7296@msgid.df7cb.de>
talks about a stack overflow with the same cause; I really think the
kernel should stop doing that.

> Also, musl does not provide a working sbrk at all, since synchronizing
> with an application's use of sbrk would introduce performance costs
> into all correct applications that don't poke at the brk.

Looking at the manpage, I can't really follow how having sbrk() would
involve a slowdown in everything?  Do you mean that musl's malloc gets
a speed bonus out of assuming it's the sole user of brk()/sbrk(), and
thus the whole region from the initial brk()point to the current
brk()point is belongs to it?  (Yeah, all (potentially) 125 MiB -
stacksize of it!)