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Date:   Sun, 30 Jan 2022 12:58:17 -0800 (PST)
From:   David Rientjes <rientjes@google.com>
To:     "Matthew Wilcox (Oracle)" <willy@infradead.org>
cc:     Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Naoya Horiguchi <naoya.horiguchi@nec.com>
Subject: Re: [PATCH] mm/hwpoison: Check the subpage, not the head page
In-Reply-To: <20220130013042.1906881-1-willy@infradead.org>
Message-ID: <dcfa1ee5-1512-5e49-92c2-4a33ab59080@google.com>
References: <20220130013042.1906881-1-willy@infradead.org>
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On Sun, 30 Jan 2022, Matthew Wilcox (Oracle) wrote:

> Hardware poison is tracked on a per-page basis, not on the head page.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
>  mm/rmap.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 6a1e8c7f6213..09b08888120e 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1553,7 +1553,7 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
>  		/* Update high watermark before we lower rss */
>  		update_hiwater_rss(mm);
>  
> -		if (PageHWPoison(page) && !(flags & TTU_IGNORE_HWPOISON)) {
> +		if (PageHWPoison(subpage) && !(flags & TTU_IGNORE_HWPOISON)) {
>  			pteval = swp_entry_to_pte(make_hwpoison_entry(subpage));
>  			if (PageHuge(page)) {
>  				hugetlb_count_sub(compound_nr(page), mm);
> @@ -1873,7 +1873,7 @@ static bool try_to_migrate_one(struct page *page, struct vm_area_struct *vma,
>  			 * memory are supported.
>  			 */
>  			subpage = page;
> -		} else if (PageHWPoison(page)) {
> +		} else if (PageHWPoison(subpage)) {
>  			pteval = swp_entry_to_pte(make_hwpoison_entry(subpage));
>  			if (PageHuge(page)) {
>  				hugetlb_count_sub(compound_nr(page), mm);

This looks correct.  Correct me if I'm wrong that this is for consistency 
and cleanup and that there is no bug being fixed by this, however.

Thanks!