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SubjectRe: [HMM v13 03/18] mm/ZONE_DEVICE/free_hot_cold_page: catch ZONE_DEVICE pages
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On 11/18/2016 11:48 PM, Jérôme Glisse wrote:
> Catch page from ZONE_DEVICE in free_hot_cold_page(). This should never
> happen as ZONE_DEVICE page must always have an elevated refcount.
>
> This is to catch refcounting issues in a sane way for ZONE_DEVICE pages.
>
> Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
> ---
> mm/page_alloc.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 0fbfead..09b2630 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2435,6 +2435,16 @@ void free_hot_cold_page(struct page *page, bool cold)
> unsigned long pfn = page_to_pfn(page);
> int migratetype;
>
> + /*
> + * This should never happen ! Page from ZONE_DEVICE always must have an
> + * active refcount. Complain about it and try to restore the refcount.
> + */
> + if (is_zone_device_page(page)) {
> + VM_BUG_ON_PAGE(is_zone_device_page(page), page);
> + page_ref_inc(page);
> + return;
> + }

This fixes an issue in the existing ZONE_DEVICE code, should not this
patch be sent separately not in this series ?

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