Re: [PATCH v3 06/20] mm, hugetlb: return a reserved page to a reserved pool if failed

[Joonsoo Kim <iamjoonsoo.kim@lge.com>]

On Fri, Sep 06, 2013 at 02:23:16PM +0900, Joonsoo Kim wrote:
> If we fail with a reserved page, just calling put_page() is not sufficient,
> because put_page() invoke free_huge_page() at last step and it doesn't
> know whether a page comes from a reserved pool or not. So it doesn't do
> anything related to reserved count. This makes reserve count lower
> than how we need, because reserve count already decrease in
> dequeue_huge_page_vma(). This patch fix this situation.
> 
> In this patch, PagePrivate() is used for tracking reservation.
> When resereved pages are dequeued from reserved pool, Private flag is
> assigned to the hugepage until properly mapped. On page returning process,
> if there is a hugepage with Private flag, it is considered as the one
> returned in certain error path, so that we should restore one
> reserve count back in order to preserve certain user's reserved hugepage.
> 
> Using Private flag is safe for the hugepage, because it doesn't use the
> LRU mechanism so that there is no other user of this page except us.
> Therefore we can use this flag safely.
> 
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> ---
> Replenishing commit message only.

Hello, Andrew.

One fix is needed, so here are v4.
What I fix is mentioned in commit message.

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