On 2016-04-12 21:58:14 +0200, reiner peterke wrote:
> Hi
>
> We have been doing some testing with Postgres (9.5.2) compiled on a Power8
> running Centos 7
>
> 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?
> after a bit of investigation we noticed that hugepagesize is har coded
> to 2MB
Note it's not actually hardcoded to some size. It's just about rounding
the size to a multiple of 2MB due to an older kernel bug:
/*
* Round up the request size to a suitable large value.
*
* Some Linux kernel versions are known to have a bug, which
causes
* mmap() with MAP_HUGETLB to fail if the request size is not a
* multiple of any supported huge page size. To work around
that, we
* round up the request size to nearest 2MB. 2MB is the most
common
* huge page page size on affected systems.
> Going further, we tried testing hugepages also on Ubuntu 16.04, also on the
> power8. On Ubuntu Postgres did not like the hugepages at all (set also to
> 16MB) and consistently crashed.
> Looking for some insight into this issue. the error from the postgres
> log on ubuntu is below. It apperas to be related to semephores.
I've a bit of a hard time believing that this is related to huge pages.
Greetings,
Andres Freund
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