Re: Problems with huge_pages and IBM Power8

On 2016-04-14 12:05:39 +0200, Bernd Helmle wrote:
>
>
> --On 12. April 2016 13:20:10 -0700 Andres Freund <andres(at)anarazel(dot)de> wrote:
>
> >> When working with huge_pages, we initially got this error.
> >>
> >> munmap(0x3efbe4000000) failed: Invalid argument
> >
> > *munmap*, not mmap failed? that's odd; because there the hugepagesize
> > shouldn't have much of an influence. If something fails it should be the
> > initial mmap. Could you show a strace of a failed start with an
> > unmodified postgres?
>
> Well, the manpage on the the buildfarm member chub says this:
>
> <snip>
> The address addr must be a multiple of the page size. All pages containing
> a part of the indicated range are unmapped, and
> subsequent references to these pages will generate SIGSEGV. It is
> not an error if the indicated range does not contain any
> mapped pages.
> </snip>

Uh, but that's something different, no? The address we pass to munmap()
is what mmap() returned. The page size bit is relevant if you want to
unmap part of a mapped region.

> Though, we haven't encountered any problems on the production machines so
> far.

That's after applying some patch to pad to a larger size?

Greetings,

Andres Freund