Re: can we optimize STACK_DEPTH_SLOP

On Fri, Jul 8, 2016 at 3:32 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Hm, after reading the man page I don't quite see how that would help?
> You'd have to already know the mapped stack address range in order to
> call the function without getting ENOMEM.

I had assumed unmapped pages would just return a 0 in the bitmap. I
suppose you could still do it by just probing one page at a time until
you find an unmapped page. In a way that's better since you can count
stack pages even if they're paged out.

Fwiw here's the pmap info from burbot (Linux Sparc64):
136 48 48 rw--- [ stack ]
136 48 48 rw--- [ stack ]
136 48 48 rw--- [ stack ]
136 48 48 rw--- [ stack ]
136 56 56 rw--- [ stack ]
136 80 80 rw--- [ stack ]
136 96 96 rw--- [ stack ]
136 112 112 rw--- [ stack ]
136 112 112 rw--- [ stack ]
576 576 576 rw--- [ stack ]
2056 2056 2056 rw--- [ stack ]

I'm actually a bit confused how to interpret these numbers. This
appears to be an 8kB pagesize architecture so is that 576*8kB or over
5MB of stack for the regexp test? But we don't know if there are any
check_stack_depth calls in that call tree?

--
greg