Re: Doc tweak for huge_pages?

On Wed, Jan 24, 2018 at 07:46:41AM +0100, Catalin Iacob wrote:
> I see Peter assigned himself as committer, some more information below
> for him to decide on the strength of the anti THP message.
Thanks for digging this up!

> And it would be good if somebody could run benchmarks on pre 4.6 and
> post 4.6 kernels. I would love to but have no access to big (or
> medium) hardware.
I should be able to do this, since I have a handful of kernels upgrades on my
todo list. Can you recommend a test ? Otherwise I'll come up with something
for pgbench.

But I think any test should be independant of and not influence the doc change
(I don't know anywhere else in the docs which talks about behaviors of specific
kernel versions, which often have vendor patches backpatched anyway).

> So maybe we should weaken the language against THP. Maybe present the
> known facts so far, even if the post 4.6 situation is vague/unknown:
> before Linux 4.6 there were repeated reports of THP problems with
> Postgres, Linux >= 4.6 might improve things but this isn't confirmed.
> And it would be good if somebody could run benchmarks on pre 4.6 and
> post 4.6 kernels. I would love to but have no access to big (or
> medium) hardware.
I think all the details should go elsewhere in the docs; config.sgml already
references this:
https://www.postgresql.org/docs/current/static/kernel-resources.html#LINUX-HUGE-PAGES
..but it doesn't currently mention "transparent" hugepages.

Justin