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

Kirill A. Shutemov
2019-10-01T10:39:41Z

On Tue, Sep 24, 2019 at 05:52:11PM -0700, Matthew Wilcox wrote:
> From: William Kucharski <william.kucharski@oracle.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@oracle.com>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.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