linux-kernel - Re: [PATCH 12/15] mm: Support removing arbitrary sized pages from mapping

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Date:   Tue, 1 Oct 2019 13:39:39 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        William Kucharski <william.kucharski@...cle.com>
Subject: Re: [PATCH 12/15] mm: Support removing arbitrary sized pages from
 mapping

On Tue, Sep 24, 2019 at 05:52:11PM -0700, Matthew Wilcox wrote:
> From: William Kucharski <william.kucharski@...cle.com>
> 
> __remove_mapping() assumes that pages can only be either base pages
> or HPAGE_PMD_SIZE.  Ask the page what size it is.

You also fixes the issue CONFIG_READ_ONLY_THP_FOR_FS=y with this patch.
The new feature makes the refcount calculation relevant not only for
PageSwapCache(). It should go to v5.4.

> 
> Signed-off-by: William Kucharski <william.kucharski@...cle.com>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>

> ---
>  mm/vmscan.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index a7f9f379e523..9f44868e640b 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -932,10 +932,7 @@ static int __remove_mapping(struct address_space *mapping, struct page *page,
>  	 * Note that if SetPageDirty is always performed via set_page_dirty,
>  	 * and thus under the i_pages lock, then this ordering is not required.
>  	 */
> -	if (unlikely(PageTransHuge(page)) && PageSwapCache(page))
> -		refcount = 1 + HPAGE_PMD_NR;
> -	else
> -		refcount = 2;
> +	refcount = 1 + compound_nr(page);
>  	if (!page_ref_freeze(page, refcount))
>  		goto cannot_free;
>  	/* note: atomic_cmpxchg in page_ref_freeze provides the smp_rmb */
> -- 
> 2.23.0
> 
> 

-- 
 Kirill A. Shutemov