linux-kernel - RE: [PATCH] mm: Introduce kernelcore=reliable option

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Date:	Fri, 30 Oct 2015 19:42:17 +0000
From:	"Luck, Tony" <tony.luck@...el.com>
To:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	"Izumi, Taku" <izumi.taku@...fujitsu.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"qiuxishi@...wei.com" <qiuxishi@...wei.com>,
	"mel@....ul.ie" <mel@....ul.ie>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"Hansen, Dave" <dave.hansen@...el.com>,
	"matt@...eblueprint.co.uk" <matt@...eblueprint.co.uk>
Subject: RE: [PATCH] mm: Introduce kernelcore=reliable option

> If each memory controller has the same distance/latency, you (your firmware) don't need
> to allocate reliable memory per each memory controller.
> If distance is problem, another node should be allocated.
>
> ...is the behavior(splitting zone) really required ?

It's useful from a memory bandwidth perspective to have allocations
spread across both memory controllers. Keeping a whole bunch of
Xeon cores fed needs all the bandwidth you can get.

Socket0 is also a problem.  We want to mirror <4GB addresses because
there is a bunch of critical stuff there (entire kernel text+data). But we
can currently only mirror one block per memory controller, so we end up
with just 2GB mirrored (the 2GB-4GB range is MMIO).  This isn't enough
for even a small machine (I have 128GB on node0 ... but that is really the
bare minimum configuration ... 2GB is only enough to cover the "struct
page" allocations for node0).  I really have to allocate some more mirror
from the other memory controller.

-Tony

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