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Date: Thu, 03 Sep 2015 08:17:02 -0400
From: Prarit Bhargava <prarit@redhat.com>
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To: "Luis R. Rodriguez" <mcgrof@suse.com>,
        Stuart Hayes <stuart.w.hayes@gmail.com>
CC: tglx@linutronix.de, mingo@redhat.com, "H. Peter Anvin" <hpa@zytor.com>,
        linux-kernel@vger.kernel.org, x86@kernel.org, mcgrof@do-not-panic.com,
        Toshi Kani <toshi.kani@hp.com>
Subject: Re: Fwd: [PATCH] x86: Use larger chunks in mtrr_cleanup
References: <55E477DE.2060106@gmail.com> <55E47B4D.1050103@gmail.com> <20150903024542.GS8051@wotan.suse.de>
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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.