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Subject: Re: [RFC][PATCH v1 11/11] mm: hwpoison: introduce
 clear_hwpoison_free_buddy_page()
To:     Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Cc:     Michal Hocko <mhocko@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        xishi.qiuxishi@alibaba-inc.com,
        Laurent Dufour <ldufour@linux.vnet.ibm.com>
References: <1541746035-13408-1-git-send-email-n-horiguchi@ah.jp.nec.com>
 <1541746035-13408-12-git-send-email-n-horiguchi@ah.jp.nec.com>
From:   Anshuman Khandual <anshuman.khandual@arm.com>
Message-ID: <d37c1be2-2069-a147-9ba8-4749cd386d0b@arm.com>
Date:   Fri, 9 Nov 2018 17:03:06 +0530
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On 11/09/2018 12:17 PM, Naoya Horiguchi wrote:
> The new function is a reverse operation of set_hwpoison_free_buddy_page()
> to adjust unpoison_memory() to the new semantics.
> 
> Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>

snip

> +
> +/*
> + * Reverse operation of set_hwpoison_free_buddy_page(), which is expected
> + * to work only on error pages isolated from buddy allocator.
> + */
> +bool clear_hwpoison_free_buddy_page(struct page *page)
> +{
> +	struct zone *zone = page_zone(page);
> +	bool unpoisoned = false;
> +
> +	spin_lock(&zone->lock);
> +	if (TestClearPageHWPoison(page)) {
> +		unsigned long pfn = page_to_pfn(page);
> +		int migratetype = get_pfnblock_migratetype(page, pfn);
> +
> +		__free_one_page(page, pfn, zone, 0, migratetype);
> +		unpoisoned = true;
> +	}
> +	spin_unlock(&zone->lock);
> +	return unpoisoned;
> +}
>  #endif
> 

Though there are multiple page state checks in unpoison_memory() leading
upto clearing HWPoison flag, the page must not be in buddy already if
__free_one_page() would be called on it.