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Date: Mon, 1 Oct 2012 11:43:11 -0400
From: Jamie Gloudon <jamie.gloudon@gmail.com>
To: Hugh Dickins <hughd@google.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: x86_64: wrong DirectMap kB
Message-ID: <20121001154311.GA2605@darkstar>
References: <20121001104652.GA1390@darkstar>
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I was also skeptical about DirectMap results added up being less than
MemTotal. I see now, Thanks for the explanation.

Jamie Gloudon

On Mon, Oct 01, 2012 at 08:23:38AM -0700, Hugh Dickins wrote:
> 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