linux-kernel - Re: [RFC 0/2] Delay initializing of large sections of memory

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Date:	Fri, 21 Jun 2013 15:40:33 -0500
From:	Nathan Zimmer <nzimmer@....com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Nathan Zimmer <nzimmer@....com>,
	Greg KH <gregkh@...uxfoundation.org>,
	"H. Peter Anvin" <hpa@...or.com>, Robin Holt <holt@....com>,
	Mike Travis <travis@....com>, Rob Landley <rob@...dley.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	linux-doc@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC 0/2] Delay initializing of large sections of memory

On Fri, Jun 21, 2013 at 01:28:11PM -0700, Yinghai Lu wrote:
> On Fri, Jun 21, 2013 at 12:19 PM, Nathan Zimmer <nzimmer@....com> wrote:
> > On 06/21/2013 02:10 PM, Yinghai Lu wrote:
> >> in this way we can keep all numa etc on the place when online ram, cpu,
> >> pci...
> >>
> >> For example if we have 32 sockets system, most time for boot is with
> >> *BIOS*
> >> instead of OS. In those kind of system boot is like this way:
> >> only first two sockets get booted from bios to OS.
> >> later use hot add every other two sockets.
> >>
> >> that will also make BIOS simpler, and it need to support hot-add for
> >> services purpose anyway.
> >>
> > Yes the hot add path was one option we looked at and it did shorten boot
> > times but the goal I had here is to get from power on to having the full
> > machine available as quick as possible. Several clients need significant
> > portions of ram for their key workloads.  So that guided my thoughts on this
> > patch.
> 
> you mean boot small number sockets + hot add still take more time?
> hot add ram still in serialize mode?
> 
> Yinghai

Yes the hot add path is still fairly serial.
lock_memory_hotplug() is still a global lock, which effectivly serializes
online pages.  Since the hotplug lock could done per node but for that to be 
effective something would need to be done with lock_system_sleep() since is
called by lock_memory_hotplug().

Nate
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