linux-kernel - Re: [patch 2/2] mm: pgtable -- Require X86

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Date:	Tue, 06 May 2014 09:28:07 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Cyrill Gorcunov <gorcunov@...nvz.org>, linux-kernel@...r.kernel.org
CC:	linux-mm@...ck.org, torvalds@...ux-foundation.org, mgorman@...e.de,
	mingo@...nel.org, steven@...inklabs.net, riel@...hat.com,
	david.vrabel@...rix.com, akpm@...ux-foundation.org,
	peterz@...radead.org, xemul@...allels.com
Subject: Re: [patch 2/2] mm: pgtable -- Require X86_64 for soft-dirty tracker

On 04/25/2014 01:10 AM, Cyrill Gorcunov wrote:
> Tracking dirty status on 2 level pages requires very ugly macros
> and taking into account how old the machines who can operate
> without PAE mode only are, lets drop soft dirty tracker from
> them for code simplicity (note I can't drop all the macros
> from 2 level pages by now since _PAGE_BIT_PROTNONE and
> _PAGE_BIT_FILE are still used even without tracker).
> 
> Linus proposed to completely rip off softdirty support on
> x86-32 (even with PAE) and since for CRIU we're not planning
> to support native x86-32 mode, lets do that.
> 
> (Softdirty tracker is relatively new feature which mostly used
>  by CRIU so I don't expect if such API change would cause problems
>  on userspace).

I have to wonder which one is more likely to actually matter on whatever
legacy 32-bit are going to remain.  This pretty much comes down to what
kind of advanced features are going to matter in deep embedded
applications in the future: checkpoint/restart or NUMA.  My guess is
that it is actually checkpoint/restart...

How much does it actually simplify to leave this feature in for PAE?  I
could care less about non-PAE... NX has pretty much killed that off cold.

	-hpa


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