linux-kernel - Re: weird DirectMap2M accounting.

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Message-ID: <alpine.DEB.2.11.1601110957390.3575@nanos>
Date:	Mon, 11 Jan 2016 09:58:01 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Dave Jones <davej@...emonkey.org.uk>
cc:	Linux Kernel <linux-kernel@...r.kernel.org>, x86@...nel.org
Subject: Re: weird DirectMap2M accounting.

On Wed, 6 Jan 2016, Dave Jones wrote:
> On Wed, Jan 06, 2016 at 07:11:41PM -0500, Dave Jones wrote:
>  > On Wed, Jan 06, 2016 at 06:55:27PM -0500, Dave Jones wrote:
>  >  > I just spotted this in /proc/meminfo on an old Core2 machine with 4G.
>  >  > 
>  >  > DirectMap2M:    18446744073709543424 kB
>  >  > 
>  >  > Looks like we subtracted 8192 from 0 somewhere.
>  >  > 
>  >  > Should split_page_count() be checking that direct_pages_count > 0 ?
>  > 
>  > Ok, this diff makes that number print out as 0.
>  > 
>  > If this looks ok, I'll submit it properly, though I'd like to better
>  > understand what's happening here. Shouldn't I have 2M pages ?
> 
> Ah. We disable them when compiling with DEBUG_PAGEALLOC.
> So this is only needed in that case.
> If people think it's worth an ifdef for those two added lines I'll add it,
> but it seems pretty benign to just always check.

Agreed.

	tglx