linux-kernel - Re: [PATCH v2 3/5] mm: Support removing arbitrary sized pages from mapping

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Date:   Thu, 17 Oct 2019 10:43:39 -0700
From:   Yang Shi <shy828301@...il.com>
To:     Song Liu <songliubraving@...com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        matthew.wilcox@...cle.com, kernel-team@...com,
        william.kucharski@...cle.com,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v2 3/5] mm: Support removing arbitrary sized pages from mapping

On Thu, Oct 17, 2019 at 9:42 AM Song Liu <songliubraving@...com> 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.
>
> Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS")
> Signed-off-by: William Kucharski <william.kucharski@...cle.com>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> Signed-off-by: Song Liu <songliubraving@...com>

Acked-by: Yang Shi <yang.shi@...ux.alibaba.com>

> ---
>  mm/vmscan.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index c6659bb758a4..f870da1f4bb7 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 */
> --
> 2.17.1
>
>