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Date: Tue, 19 Feb 2013 10:56:27 -0800 (PST)
From: Hugh Dickins <hughd@google.com>
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To: Ric Mason <ric.masonn@gmail.com>
cc: Li Haifeng <omycle@gmail.com>, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: Should a swapped out page be deleted from swap cache?
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On Tue, 19 Feb 2013, Ric Mason wrote:
> 
> There is a call of try_to_free_swap in function swap_writepage, if
> swap_writepage is call from shrink_page_list path, PageSwapCache(page) ==
> trure, PageWriteback(page) maybe false, page_swapcount(page) == 0, then will
> delete the page from swap cache and free swap slot, where I miss?

That's correct.  PageWriteback is sure to be false there.  page_swapcount
usually won't be 0 there, but sometimes it will be, and in that case we
do want to delete from swap cache and free the swap slot.

Hugh