Re: Problems with huge_pages and IBM Power8

--On 12. April 2016 13:20:10 -0700 Andres Freund <andres@anarazel.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>

There are other production machines running on this POWER8 machine, all
have huge pages activated and i've seen this message several times, but
afair only during initdb and when stopping the server. No crashes. 

Indeed, I had the exactly same patch than Reiner, when investigating this,
but i couldn't find an easy way to make it somehow automatic for other page
sizes (e.g. on large Intel machines you can have even 1G Pages).

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

-- 
Thanks
Bernd