Re: Doc tweak for huge_pages?

On Mon, Jan 22, 2018 at 03:54:26PM +1300, Thomas Munro wrote:
> On Fri, Jan 12, 2018 at 1:12 PM, Thomas Munro
> <thomas(dot)munro(at)enterprisedb(dot)com> wrote:
> > On Tue, Jan 9, 2018 at 6:24 AM, Catalin Iacob <iacobcatalin(at)gmail(dot)com> wrote:
> > 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?
>
> Now that the Windows huge pages patch has landed, here is a rebase. I
> took your alternative and tweaked it a tiny bit more. Thoughts?

+ <para>
+ Note that, besides explicitly requesting huge pages via
+ <varname>huge_pages</varname>,
=> I would just say:
"Note that, besides huge pages requested explicitly, ..."

+ In Linux this automatic use is
=> ON Linux comma?

+ called "transparent huge pages" and is not enabled by default in
+ popular distributions as of the time of writing, but since transparent

=> really ? I don't know if I've ever seen it not enabled. In any case,
that's a strong statement to make (to be disabled in ALL popular distributions).

I checked all our servers, including centos6 and ubuntu t-LTS and x-LTS. On a
limited few where it was disabled, I'd explicitly done so.

On a server on which I just installed ubuntu-x LTS, with 4.13.0-26-generic:
pryzbyj(at)gta-ubuntu:~$ cat /sys/kernel/mm/transparent_hugepage/enabled
always [madvise] never

https://github.com/torvalds/linux/commit/13ece886d99cd668483113f7238e419d5331af26
=> the compile time default is to disable, but (if enabled at compile time),
the runtime default is "always".

On centos7
Linux template0 3.10.0-693.11.6.el7.x86_64 #1 SMP Thu Jan 4 01:06:37 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
$ cat /sys/kernel/mm/transparent_hugepage/enabled
[always] madvise never
$ grep TRANS /boot/config-3.10.0-693.11.6.el7.x86_64
CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE=y
CONFIG_TRANSPARENT_HUGEPAGE=y
CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS=y
# CONFIG_TRANSPARENT_HUGEPAGE_MADVISE is not set

https://blog.nelhage.com/post/transparent-hugepages/
=> It is enabled (”enabled=always”) by default in most Linux distributions.

Justin