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Date: Tue, 15 Sep 2015 09:58:47 +0300
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To: Rasmus Lerdorf <rasmus@lerdorf.com>
Cc: Anatol Belski <anatol.php@belski.net>, Anatol Belski <ab@php.net>, 
	Kalle Sommer Nielsen <kalle@php.net>, Xinchen Hui <xinchen.h@zend.com>, Nikita Popov <nikita.ppv@gmail.com>, 
	Zeev Suraski <zeev@zend.com>, Andi Gutmans <andi@zend.com>, PHP Internals <internals@lists.php.net>
Content-Type: multipart/alternative; boundary=001a11431e76a80a3c051fc3b6ba
Subject: Re: [PHP-DEV] Re: [PHP-CVS] com php-src: Added an experemental
 ability to move PHP code pages (PHP TEXT segment) into HUGE pages. PHP should
 be configured and built with --enable-huge-code-pages, OS should be
 configured to provide huge pages. It's possibl
From: dmitry@zend.com (Dmitry Stogov)

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On Tue, Sep 15, 2015 at 4:31 AM, Rasmus Lerdorf <rasmus@lerdorf.com> wrote:

> On 09/14/2015 02:13 PM, Anatol Belski wrote:
> >
> >
> >> -----Original Message-----
> >> From: Dmitry Stogov [mailto:dmitry@zend.com]
> >> Sent: Monday, September 14, 2015 10:37 PM
> >> To: Anatol Belski <anatol.php@belski.net>
> >> Cc: Anatol Belski <ab@php.net>; Kalle Sommer Nielsen <kalle@php.net>;
> >> Rasmus Lerdorf <rasmus@lerdorf.com>; Xinchen Hui <xinchen.h@zend.com>;
> >> Nikita Popov <nikita.ppv@gmail.com>; Zeev Suraski <zeev@zend.com>; Andi
> >> Gutmans <andi@zend.com>; PHP Internals <internals@lists.php.net>
> >> Subject: Re: [PHP-DEV] Re: [PHP-CVS] com php-src: Added an experemental
> >> ability to move PHP code pages (PHP TEXT segment) into HUGE pages. PHP
> >> should be configured and built with --enable-huge-code-pages, OS should
> be
> >> configured to provide huge pages. It's possibl
> >>
> >>>
> >>> With the new huge memory pages feature I'd suggest a bit softer -
> >>> enabling its building, but setting opcache.enable_huge_code_pages=0 by
> >> default.
> >>
> >>
> >> OK.
> >>
> >>
> >>> Then it can be easy enable and give one more intermediate step for pre
> >>> testing and go into RC4 completely if ok.
> >>
> >>
> >> In general we may get build problems on some platforms...
> >>
> >>
> >>> What do you think?
> >>>
> >>
> >> I didn't get, do you like to delay this for RC4? or enable it at
> compile time and
> >> disable at run-time by default for RC3?
> >> I agree with both.
> >>
> > I was suggesting the latter - build and disable at run-time. With RC4 I
> meant - as it's run-time enabled by default currently, that could be turned
> on by default in RC4 if everything was well in RC3.
> >
> > Regarding possible build issues you mention - probably some magic in
> config.m4 could disable huge pages? I wasn't aware, but probably yep - like
> FreeBSD or OSX likely to not to have the sys/prctl.h . This could be a
> reason for delaying till RC4, but it's actually easy solved doing some test
> compilation in config.m4 . I'd see build + disable on run-time in RC3 as a
> better move because it turns the test circle earlier which is good
> considering there are only 4 RCs to go yet.
>
> As long as we fail gracefully when compiled with hugepage support and
> then run on a system that doesn't have any hugepages configured. These
> days the build box and the production execution box are rarely the same
> machine.
>

Yeah. This is transparent solution. At first it's disabled by default by
opcache.huge_code_pages=0. At second, it should work without problem if OS
doesn't provide huge pages.


>
> Redhat enables THP by default and has for a while, but I know lots of
> admins that disable this feature right away on production machines. I
> don't think it is default on Ubuntu, but at least they have hugepage
> tools to make it easy to configure. And from a quick look at Debnian
> (jessie) it wasn't obvious how to get hugepages working. I don't see a
> package for hugeadm offhand. The kernel supports it, obviously, but you
> need to take some steps to configure them.
>

PHP prefers using regular Huge Pages and may fail back to THP (Transparent
Huge Pages).
So THP don't have to be enabled.


>
> Which means we also need to spend a bit of time documenting how to
> enable hugepages at the OS level for the various operating systems to go
> along with this feature.
>

Right. Manual OS configuration is required. See
https://wiki.debian.org/Hugepages#Enabling_HugeTlbPage
Steps (3) and (4) are optional.

Thanks. Dmitry.


>
> -Rasmus
>
>

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