Message-ID: <4E035DD1.1030603@kpanic.de>
Date: Thu, 23 Jun 2011 17:37:53 +0200
From: Stefan Assmann <sassmann@kpanic.de>
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To: Matthew Garrett <mjg59@srcf.ucam.org>
CC: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        akpm@linux-foundation.org, tony.luck@intel.com, andi@firstfloor.org,
        mingo@elte.hu, hpa@zytor.com, rick@vanrein.org, rdunlap@xenotime.net
Subject: Re: [PATCH v2 0/3] support for broken memory modules (BadRAM)
References: <1308741534-6846-1-git-send-email-sassmann@kpanic.de> <20110623133950.GB28333@srcf.ucam.org> <4E0348E0.7050808@kpanic.de> <20110623141222.GA30003@srcf.ucam.org>
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On 23.06.2011 16:12, Matthew Garrett wrote:
> On Thu, Jun 23, 2011 at 04:08:32PM +0200, Stefan Assmann wrote:
>> On 23.06.2011 15:39, Matthew Garrett wrote:
>>> Would it be more reasonable to do this in the bootloader? You'd ideally 
>>> want this to be done as early as possible in order to avoid awkward 
>>> situations like your ramdisk ending up in the bad RAM area.
>>
>> Not sure what exactly you are suggesting here. The kernel somehow needs
>> to know what memory areas to avoid so we supply this information via
>> kernel command line.
>> What the bootloader could do is to allow the kernel/initrd to be loaded
>> at an alternative address. That's briefly mentioned in the BadRAM
>> Documentation as well. Is that what you mean or am I missing something?
> 
> For EFI booting we just hand an e820 map to the kernel. It ought to be 
> easy enough to add support for that to the 16-bit entry point as well. 
> Then the bootloader just needs to construct an e820 map of its own. I 
> think grub2 actually already has some support for this. The advantage of 
> this approach is that the knowledge of bad memory only has to exist in 
> one place (ie, the bootloader) - the kernel can remain blisfully 
> unaware.
> 

According to Rick's reply in this thread a damaged row in a DIMM can
easily cause a few thousand entries in the e820 table because it doesn't
handle patterns. So the question I'm asking is, is it acceptable to
have an e820 table with thousands maybe ten-thousands of entries?
I really have no idea of the implications, maybe somebody else can
comment on that.

  Stefan
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