[QUESTION] balloon page isolation needs LRU lock?

[Joonsoo Kim]

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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