Re: [PATCH v2] mm: hwpoison: adjust for new thp refcounting

From: Kirill A. Shutemov
Date: Fri Nov 06 2015 - 05:34:51 EST


On Fri, Nov 06, 2015 at 05:03:12PM +0900, Naoya Horiguchi wrote:
> Some mm-related BUG_ON()s could trigger from hwpoison code due to recent
> changes in thp refcounting rule. This patch fixes them up.
>
> In the new refcounting, we no longer use tail->_mapcount to keep tail's
> refcount, and thereby we can simplify get/put_hwpoison_page().
>
> And another change is that tail's refcount is not transferred to the raw
> page during thp split (more precisely, in new rule we don't take refcount
> on tail page any more.) So when we need thp split, we have to transfer the
> refcount properly to the 4kB soft-offlined page before migration.
>
> thp split code goes into core code only when precheck (total_mapcount(head)
> == page_count(head) - 1) passes to avoid useless split, where we assume that
> one refcount is held by the caller of thp split and the others are taken
> via mapping. To meet this assumption, this patch moves thp split part in
> soft_offline_page() after get_any_page().
>
> Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
> ---
> ChangeLog v1->v2:
> - leave put_hwpoison_page() as a macro
>
> - based on mmotm-2015-10-21-14-41 + Kirill's "[PATCH 0/4] Bugfixes for THP
> refcounting" series.
> ---
> include/linux/mm.h | 1 +
> mm/memory-failure.c | 75 +++++++++++++++------------------------------------
> 2 files changed, 23 insertions(+), 53 deletions(-)
>
> diff --git mmotm-2015-10-21-14-41/include/linux/mm.h mmotm-2015-10-21-14-41_patched/include/linux/mm.h
> index a36f9fa..51e3ffe 100644
> --- mmotm-2015-10-21-14-41/include/linux/mm.h
> +++ mmotm-2015-10-21-14-41_patched/include/linux/mm.h
> @@ -2173,6 +2173,7 @@ extern int memory_failure(unsigned long pfn, int trapno, int flags);
> extern void memory_failure_queue(unsigned long pfn, int trapno, int flags);
> extern int unpoison_memory(unsigned long pfn);
> extern int get_hwpoison_page(struct page *page);
> +#define put_hwpoison_page(page) put_page(page)
> extern void put_hwpoison_page(struct page *page);

This line should be removed.

Otherwise looks good to me.

Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>

--
Kirill A. Shutemov
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