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

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Message-ID: <BANLkTinN0EOH=OMQ8idG7Xt5OufU-6Rn3A@mail.gmail.com>
Date:	Wed, 29 Jun 2011 14:24:41 -0700
From:	Tony Luck <tony.luck@...el.com>
To:	Craig Bergstrom <craigb@...gle.com>
Cc:	linux-kernel@...r.kernel.org, fa.linux.kernel@...glegroups.com,
	Rick van Rein <rick@...rein.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Stefan Assmann <sassmann@...nic.de>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"rdunlap@...otime.net" <rdunlap@...otime.net>,
	Nancy Yuen <yuenn@...gle.com>,
	Michael Ditto <mditto@...gle.com>
Subject: Re: [PATCH v2 0/3] support for broken memory modules (BadRAM)

One extra consideration for this whole proposal ...

Is the "physical address" a stable enough representation of the location
of the faulty memory cells?

On high end systems I can see a number of ways where the mapping
from cells to physical address may change across reboot:

1) System support redundant memory (rank sparing or mirroring)
2) BIOS self test removes some memory from use
3) A multi-node system elects a different node to be boot-meister,
which results in reshuffling of the address map.

If any of these can happen: then it doesn't matter whether we have
a list of addresses, or a pattern that expands to a list of addresses.
We'll still mark some innocent memory as bad, and allow some known
bad memory to be used - because our "addresses" no longer correspond
to the bad memory cells.

-Tony
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