linux-kernel - Re: [PATCH 06/43] mm: numa: Make pte_numa() and pmd

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Date:	Fri, 16 Nov 2012 19:04:04 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Hugh Dickins <hughd@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 06/43] mm: numa: Make pte_numa() and pmd_numa() a generic
 implementation

* Mel Gorman <mgorman@...e.de> wrote:

> That said, your approach just ends up being heavier. [...]

Well, it's more fundamental than just whether to inline or not 
(which I think should be a separate optimization and I won't 
object to two-instruction variants the slightest) - but you 
ended up open-coding change_protection() 
via:

   change_prot_numa_range() et al

which is a far bigger problem...

Do you have valid technical arguments in favor of that 
duplication?

If you just embrace the PROT_NONE reuse approach of numa/core 
then 90% of the differences in your tree will disappear and 
you'll have a code base very close to where numa/core was 3 
weeks ago already, modulo a handful of renames.

It's not like PROT_NONE will go away anytime soon.

PROT_NONE is available on every architecture, and we use the 
exact semantics of it in the scheduler, we just happen to drive 
it from a special worklet instead of a syscall, and happen to 
have a callback to the faults when they happen...

Please stay open to that approach.

Thanks,

	Ingo
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