linux-kernel - Re: [PATCH 1/2] numa, mm: drop redundant check in do_huge_pmd_numa

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Message-ID: <1351256885.16863.62.camel@twins>
Date:	Fri, 26 Oct 2012 15:08:05 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:	linux-mm@...ck.org, Will Deacon <will.deacon@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] numa, mm: drop redundant check in
 do_huge_pmd_numa_page()

On Fri, 2012-10-26 at 15:54 +0300, Kirill A. Shutemov wrote:
> From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> 
> We check if the pmd entry is the same as on pmd_trans_huge() in
> handle_mm_fault(). That's enough.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

Ah indeed, Will mentioned something like this on IRC as well, I hadn't
gotten around to looking at it -- now have, thanks!

Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>

That said, where in handle_mm_fault() do we wait for a split to
complete? We have a pmd_trans_huge() && !pmd_trans_splitting(), so a
fault on a currently splitting pmd will fall through.

Is it the return from the fault on unlikely(pmd_trans_huge()) ?

I'm probably missing something obvious..
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