linux-kernel - RE: [PATCH v2 0/3] support for broken memory modules (BadRAM)

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Date:	Fri, 24 Jun 2011 09:40:51 -0700
From:	"Luck, Tony" <tony.luck@...el.com>
To:	"H. Peter Anvin" <hpa@...or.com>, Rick van Rein <rick@...rein.org>
CC:	Craig Bergstrom <craigb@...gle.com>,
	Andi Kleen <andi@...stfloor.org>,
	Stefan Assmann <sassmann@...nic.de>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"rdunlap@...otime.net" <rdunlap@...otime.net>
Subject: RE: [PATCH v2 0/3] support for broken memory modules (BadRAM)

> > I am very curious about your findings.  Independently of those, I am in
> > favour of a patch that enables longer e820 tables if it has no further
> > impact on speed or space.
> > 
>
> That is already in the mainline kernel, although only if fed from the
> boot loader (it was developed in the context of mega-NUMA machines); the
> stub fetching from INT 15h doesn't use this at the moment.

Does it scale?  Current X86 systems go up to about 2TB - presumably
in the form of 256 8GB DIMMs (or maybe 512 4GB ones).  If a faulty
row or column on a DIMM can give rise to 4K bad pages, then these
large systems could conceivably have 1-2 million bad pages (while
still being quite usable - a loss of 4-8G from a 2TB system is down
in the noise).  Can we handle a 2 million entry e820 table? Do we
want to?

Perhaps we may end up with a composite solution. Use e820 to map out
the bad pages below some limit (like 4GB). Preferably in the boot loader
so it can find a range of good memory to load the kernel. Then use
badRAM patterns for addresses over 4GB for Linux to avoid bad pages
by flagging their page structures.

-Tony
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