Re: [PATCH 0/9] Hugepage migration (v2)

[Andi Kleen]

> When get_user_pages_fast() is called before try_to_unmap(),
> direct I/O code increments refcount on the target page.
> Because this refcount is not associated to the mapping,
> migration code will find remaining refcounts after try_to_unmap()
> unmaps all mappings. Then refcount check decides migration to fail,
> so direct I/O is continued safely.

This would imply that direct IO can make migration fail arbitarily.
Also not good. Should we add some retries, at least for the soft offline
case?

-Andi

-- 
ak@xxxxxxxxxxxxxxx -- Speaking for myself only.
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