linux-kernel - Re: Fwd: [PATCH] x86: Use larger chunks in mtrr

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Message-ID: <55E83A3E.3030000@redhat.com>
Date:	Thu, 03 Sep 2015 08:17:02 -0400
From:	Prarit Bhargava <prarit@...hat.com>
To:	"Luis R. Rodriguez" <mcgrof@...e.com>,
	Stuart Hayes <stuart.w.hayes@...il.com>
CC:	tglx@...utronix.de, mingo@...hat.com,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	x86@...nel.org, mcgrof@...not-panic.com,
	Toshi Kani <toshi.kani@...com>
Subject: Re: Fwd: [PATCH] x86: Use larger chunks in mtrr_cleanup



On 09/02/2015 10:45 PM, Luis R. Rodriguez wrote:
> On Mon, Aug 31, 2015 at 11:05:33AM -0500, Stuart Hayes wrote:
>> Increase the range of chunk sizes tried in mtrr_cleanup() so it is able
>> to map large memory configs into MTRRs.
>>
>> Currently, mtrr_cleanup() will fail with large memory configurations,
>> because it limits chunk_size to 2GB, which means that each MTRR can only
>> cover 2GB of memory.  With a memory size of, say, 256GB, and ten variable
>> MTRRs (such as some recent Intel CPUs have), it is not possible to set up
>> the MTRRs to cover all of memory.
> 
> Linux drivers no longer use MTRR so why is the cleanup needed, ie, what would
> happen if the cleanup is just skipped in your case ?

The infiniband & video drivers still use MTRR (or at least it was my
understanding that they do).  In any case, Stuart -- could you try booting with
'disable_mtrr_cleanup' as a kernel parameter?

P.
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