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Date: Mon, 14 May 2012 16:55:36 +0800
From: Cong Wang <xiyou.wangcong@gmail.com>
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Subject: Re: [PATCH 1/10] shmem: replace page if mapping excludes its zone
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To: Hugh Dickins <hughd@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, Christoph Hellwig <hch@infradead.org>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, Alan Cox <alan@lxorguk.ukuu.org.uk>, Stephane Marchesin <marcheu@chromium.org>, Andi Kleen <andi@firstfloor.org>, Dave Airlie <airlied@gmail.com>, Daniel Vetter <ffwll.ch@google.com>, Rob Clark <rob.clark@linaro.org>, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org

On 05/12/2012 07:59 PM, Hugh Dickins wrote:
> +	VM_BUG_ON(!PageLocked(oldpage));
> +	__set_page_locked(newpage);
> +	VM_BUG_ON(!PageUptodate(oldpage));
> +	SetPageUptodate(newpage);
> +	VM_BUG_ON(!PageSwapBacked(oldpage));
> +	SetPageSwapBacked(newpage);
> +	VM_BUG_ON(!swap_index);
> +	set_page_private(newpage, swap_index);
> +	VM_BUG_ON(!PageSwapCache(oldpage));
> +	SetPageSwapCache(newpage);
> +

Are all of these VM_BUG_ON's necessary?

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