linux-kernel - Re: [PATCHv2, RFC 11/30] thp, mm: handle tail pages in page_cache_get

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Date:	Fri, 05 Apr 2013 12:03:17 +0800
From:	Ric Mason <ric.masonn@...il.com>
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: [PATCHv2, RFC 11/30] thp, mm: handle tail pages in page_cache_get_speculative()

Hi Kirill,
On 03/15/2013 01:50 AM, Kirill A. Shutemov wrote:
> From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
>
> For tail page we call __get_page_tail(). It has the same semantics, but
> for tail page.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> ---
>   include/linux/pagemap.h |    4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index 3521b0d..408c4e3 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -159,6 +159,9 @@ static inline int page_cache_get_speculative(struct page *page)

What's the different between page_cache_get_speculative and page_cache_get?

>   {
>   	VM_BUG_ON(in_interrupt());
>   
> +	if (unlikely(PageTail(page)))
> +		return __get_page_tail(page);
> +
>   #ifdef CONFIG_TINY_RCU
>   # ifdef CONFIG_PREEMPT_COUNT
>   	VM_BUG_ON(!in_atomic());
> @@ -185,7 +188,6 @@ static inline int page_cache_get_speculative(struct page *page)
>   		return 0;
>   	}
>   #endif
> -	VM_BUG_ON(PageTail(page));
>   
>   	return 1;
>   }

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