linux-kernel - Re: [PATCHv4 31/39] thp: consolidate code between handle_mm_fault() and do_huge_pmd_anonymous

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Message-ID: <519C0573.4030808@sr71.net>
Date:	Tue, 21 May 2013 16:38:27 -0700
From:	Dave Hansen <dave@...1.net>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
CC:	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Hugh Dickins <hughd@...gle.com>,
	Wu Fengguang <fengguang.wu@...el.com>, Jan Kara <jack@...e.cz>,
	Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org,
	Andi Kleen <ak@...ux.intel.com>,
	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Hillf Danton <dhillf@...il.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCHv4 31/39] thp: consolidate code between handle_mm_fault()
 and do_huge_pmd_anonymous_page()

On 05/11/2013 06:23 PM, Kirill A. Shutemov wrote:
> From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> 
> do_huge_pmd_anonymous_page() has copy-pasted piece of handle_mm_fault()
> to handle fallback path.
> 
> Let's consolidate code back by introducing VM_FAULT_FALLBACK return
> code.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> ---
>  include/linux/huge_mm.h |    3 ---
>  include/linux/mm.h      |    3 ++-
>  mm/huge_memory.c        |   31 +++++--------------------------
>  mm/memory.c             |    9 ++++++---
>  4 files changed, 13 insertions(+), 33 deletions

Wow, nice diffstat!

This and the previous patch can go in the cleanups pile, no?

> @@ -3788,9 +3788,12 @@ retry:
>  	if (!pmd)
>  		return VM_FAULT_OOM;
>  	if (pmd_none(*pmd) && transparent_hugepage_enabled(vma)) {
> +		int ret = 0;
>  		if (!vma->vm_ops)
> -			return do_huge_pmd_anonymous_page(mm, vma, address,
> -							  pmd, flags);
> +			ret = do_huge_pmd_anonymous_page(mm, vma, address,
> +					pmd, flags);
> +		if ((ret & VM_FAULT_FALLBACK) == 0)
> +			return ret;

This could use a small comment about where the code flow is going, when
and why.  FWIW, I vastly prefer the '!' form in these:

	if (!(ret & VM_FAULT_FALLBACK))
--
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