On Mon, Nov 26, 2018 at 03:23:37PM -0800, Hugh Dickins wrote:
> Huge tmpfs testing showed that although collapse_shmem() recognizes a
> concurrently truncated or hole-punched page correctly, its handling of
> holes was liable to refill an emptied extent. Add check to stop that.
>
> Fixes: f3f0e1d2150b2 ("khugepaged: add support of collapse for tmpfs/shmem pages")
> Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx # 4.8+
I'm not yet comfortable with XArray API. Matthew, what is your take on the patch?
> ---
> mm/khugepaged.c | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index c13625c1ad5e..2070c316f06e 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -1359,6 +1359,17 @@ static void collapse_shmem(struct mm_struct *mm,
>
> VM_BUG_ON(index != xas.xa_index);
> if (!page) {
> + /*
> + * Stop if extent has been truncated or hole-punched,
> + * and is now completely empty.
> + */
> + if (index == start) {
> + if (!xas_next_entry(&xas, end - 1)) {
> + result = SCAN_TRUNCATED;
> + break;
> + }
> + xas_set(&xas, index);
> + }
> if (!shmem_charge(mapping->host, 1)) {
> result = SCAN_FAIL;
> break;
> --
> 2.20.0.rc0.387.gc7a69e6b6c-goog
>
--
Kirill A. Shutemov
