Re: __alloc_init_space

> Hi!,  I found a nice way to import DJB alloc trick in dietlibc.
> In qmail DJB uses a static buffer of 4K in alloc.c.  After using
> it is impossible to free the buffer!
> 
> I want to add such static buffer in programs with arbitrary length.

 Please don't.
 This feature works well for DJB (and a small number of other people)
because his coding style is focused on very short-lived programs, that
either exit or exec after zero, one or two malloc()s; the static buffer
trick allows these programs to not allocate anything on the heap, save
a few system calls and give a few guarantees ("program does not dynamically
allocate memory"). This is a clever, but minor, optimization.

 However, no matter how smart it is, this coding style is very specific
and a libc should be optimized for the generic case. Unfortunately, in
the generic case, the static buffer trick is actually detrimental, because
it's impossible to reclaim the 4 kB once they're used. It's one page per
executable, and it can add up.
 The diet libc implements malloc()/free() with mmap()/munmap(). This is
simple and fast, and works. And the kernel can actually reclaim a page
that has been unmapped ! This is much more useful in the general case.

 Using the static buffer trick should be a case-by-case decision, not a
system-wide decision. It belongs to the application (just as it is in
djbware right now), not to the libc.

-- 
 Laurent