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Date: Mon, 1 Oct 2012 08:23:38 -0700 (PDT)
From: Hugh Dickins <hughd@google.com>
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To: Jamie Gloudon <jamie.gloudon@gmail.com>
cc: linux-kernel@vger.kernel.org
Subject: Re: x86_64: wrong DirectMap kB
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On Mon, 1 Oct 2012, Jamie Gloudon wrote:
> 
>  Interesting. I am able to reproduce the same problem as you using mem=700M, which shows: 
> 
> DirectMap4k:        4096 kB
> DirectMap2M:    18446744073709547520 kB
> 
> However, it appears to be normal without the boot parameter:
> 
> DirectMap4k:        4096 kB
> DirectMap2M:    15708160 kB

It appears to be normal because the calculations haven't wrapped around,
but if you compare with 3.4 or before, I think you'll find that it
still adds up to too little.

> 
> What does your output looks like with the full amount on 3.6?

On 3.6:

MemTotal:        8060528 kB
...
DirectMap4k:        2048 kB
DirectMap2M:     7229440 kB

So it's showing significantly less direct mapped than is included
in MemTotal (which itself omits some areas of reserved memory).

Whereas on 3.4:

MemTotal:        8060760 kB
...
DirectMap4k:        4096 kB
DirectMap2M:     8275968 kB

Hugh