Re: [PATCH v2 5/5] mm/hwpoison: replace most of put_page in memory error handling by put_hwpoison_page

From: Wanpeng Li
Date: Wed Aug 12 2015 - 05:13:51 EST

On 8/12/15 4:55 PM, Naoya Horiguchi wrote:
> On Mon, Aug 10, 2015 at 07:28:23PM +0800, Wanpeng Li wrote:
>> Replace most of put_page in memory error handling by put_hwpoison_page,
>> except the ones at the front of soft_offline_page since the page maybe
>> THP page and the get refcount in madvise_hwpoison is against the single
>> 4KB page instead of the logic in get_hwpoison_page.
>> Signed-off-by: Wanpeng Li <>
> # Sorry for my late response.
> If I read correctly, get_user_pages_fast() (called by madvise_hwpoison)
> for a THP tail page takes a refcount from each of head and tail page.
> gup_huge_pmd() does this in the fast path, and get_page_foll() does this
> in the slow path (maybe via the following code path)
> get_user_pages_unlocked
> __get_user_pages_unlocked
> __get_user_pages_locked
> __get_user_pages
> follow_page_mask
> follow_trans_huge_pmd (with FOLL_GET set)
> get_page_foll
> So this should be equivalent to what get_hwpoison_page() does for thp pages
> with regard to refcounting.
> And I'm expecting that a refcount taken by get_hwpoison_page() is released
> by put_hwpoison_page() even if the page's status is changed during error
> handling (the typical (or only?) case is successful thp split.)

Indeed. :-)

> So I think you can apply put_hwpoison_page() for 3 more callsites in
> mm/memory-failure.c.

I have already done this in my patch.

> - "soft offline: %#lx page already poisoned" case (you mentioned above)
> - "soft offline: %#lx: failed to split THP" case (you mentioned above)

You are right, I will send a patch rebased on this one since they are

Wanpeng Li

> Thanks,
> Naoya Horiguchi

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