Re: Doc tweak for huge_pages?

On Tue, Jan 9, 2018 at 6:24 AM, Catalin Iacob <iacobcatalin(at)gmail(dot)com> wrote:
> On Fri, Dec 1, 2017 at 10:09 PM, Thomas Munro
> <thomas(dot)munro(at)enterprisedb(dot)com> wrote:
>>> On 11/30/17 23:35, Thomas Munro wrote:
>>>> Hmm. Yeah, it does, but apparently it's not so transparent. So if we
>>>> mention that we'd better indicate in the same paragraph that you
>>>> probably don't actually want to use it. How about the attached?
>
> Here's a review for v3.

Thanks!

> I find that the first paragraph is an improvement as it's more precise.
>
> What I didn't like about the second paragraph is that it pointed out
> Linux transparent huge pages too favorably while they are actually
> known to cause big (huge?, pardon the pun) issues (as witnessed in
> this thread as well). v3 basically says "in Linux it can be
> transparent or explicit and explicit is faster than transparent".
> Reading that, and seeing that explicit needs tweaking of kernel
> parameters and so on, one might very well conclude "I'll use the
> slightly-slower-but-still-better-than-nothing transparent version".
>
> So I tried to redo the second paragraph and ended up with the
> attached. Rationale for the changes:
> * changed "this feature" to "explicitly requesting huge pages" to
> contrast with the automatic one described below
> * made the wording of Linux THP more negative (but still with some
> wiggle room for future kernel versions which might improve THP),
> contrasting with the positive explicit request from this GUC
> * integrated your mention of other OSes with automatic huge pages
> * moved the new text to the last paragraph to lower its importance
>
> What do you think?

I don't know enough about this to make such a strong recommendation
myself, which is why I was only trying to report that bad performance
had been observed on some version, not that you shouldn't do it. Any
other views on this stronger statement?

--
Thomas Munro
http://www.enterprisedb.com