linux-kernel - [QUESTION] balloon page isolation needs LRU lock?

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Message-ID: <20131206085331.GA24706@lge.com>
Date:	Fri, 6 Dec 2013 17:53:31 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Rafael Aquini <aquini@...hat.com>
Cc:	Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: [QUESTION] balloon page isolation needs LRU lock?

Hello, Rafael.

I looked at some compaction code and found that some oddity about
balloon compaction. In isolate_migratepages_range(), if we meet
!PageLRU(), we check whether this page is for balloon compaction.
In this case, code needs locked. Is the lock really needed? I can't find
any relationship between balloon compaction and LRU lock.

Second question is that in above case if we don't hold a lock, we
skip this page. I guess that if we meet balloon page repeatedly, there
is no change to run isolation. Am I missing?

Please let me know what I am missing.

Thanks in advance.
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