Re: munmap() failure due to sloppy handling of hugepage size

On 2016-10-12 16:33:38 -0400, Tom Lane wrote:
> Andres Freund <andres(at)anarazel(dot)de> writes:
> > On October 12, 2016 1:25:54 PM PDT, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> >> A little bit of research suggests that on Linux the thing to do would
> >> be to get the actual default hugepage size by reading /proc/meminfo and
> >> looking for a line like "Hugepagesize: 2048 kB".
>
> > We had that, but Heikki ripped it out when merging... I think you're supposed to use /sys to get the available size.
>
> According to
> https://www.kernel.org/doc/Documentation/vm/hugetlbpage.txt
> looking into /proc/meminfo is the longer-standing API and thus is
> likely to work on more kernel versions.

MAP_HUGETLB, which we rely on for hugepage support, is newer than the
introducing the /sys stuff.

> Also, if you look into /sys then you are going to see multiple
> possible values and it's not clear how to choose the right one.

That's a fair point. It'd probably be good to use the largest we can,
bounded by a percentage of max waste or such. But that's likely
something for another day.

Regards,

Andres