linux-kernel - Re: Should a swapped out page be deleted from swap cache?

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Message-ID: <alpine.LNX.2.00.1302191050330.2248@eggly.anvils>
Date:	Tue, 19 Feb 2013 10:56:27 -0800 (PST)
From:	Hugh Dickins <hughd@...gle.com>
To:	Ric Mason <ric.masonn@...il.com>
cc:	Li Haifeng <omycle@...il.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: Should a swapped out page be deleted from swap cache?

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
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