[RFC v3] fiber: Increase default stack size

[Cyrill Gorcunov]

On Tue, Feb 26, 2019 at 11:58:52AM +0300, Vladimir Davydov wrote:
...
> > 
> > https://github.com/tarantool/tarantool/issues/3418
> 
> Forgot to tell you during the previous review round: we don't put a full
> link in the commit message. Instead we write:
> 
> Closes #3418

OK

> 
> We put the link after the diff separator (---) so as a reviewer can
> easily open it.
> 
> > ---
> > Vladimir, take a look please. That is what you mean?
> 
> Yes.
> 
> > I'm not yet familiar with slab engine, does it allocates
> > pages on lazy fashion or we need to pass 'dontneed' on
> > first fiber creation too?
> 
> Oops, you're right, good catch! The allocator may poison slab if NDEBUG
> is unset. So we can either
> 
>  - Madvise slab on fiber creation, at least in NDEBUG mode. Simple, but
>    depends on the allocator internals.
>  - Patch the 'small' library to make the allocator do madvise for us.
>    IMO it would look better, but would clutter the allocator API.
>  - Don't use 'small' allocator at all for default slab allocations, and
>    simply mmap stack and link them in a free list (is it OK to mmap a
>    few MB chunk per each fiber?).
> 
> I'm inclined to choose the last option. I'll discuss the options with
> others today and follow-up.

Will continue at the evening. Also note that stack is special and
we better should not pass arbitrary sizes to allocate even for
custom stacks, they all _must_ be PAGE_SIZE aligned (or call it
PAGE_SIZE orders if you prefer :) Anything else make madvise
idea useless since kernel requires madvise args to be page
aligned which is understandable due to hardware.

> > 
> > Also should not we give user a way to configure this early
> > params, maybe via getenv?
> 
> May be, but this can definitely be done later if we really need it.
OK