Re: [PATCH v1 01/11] memory-failure: fetch compound_head after pgmap_pfn_valid()

[Dan Williams <dan.j.williams@intel.com>]

On Thu, Mar 25, 2021 at 4:10 PM Joao Martins <joao.m.martins@oracle.com> wrote:
>
> memory_failure_dev_pagemap() at the moment assumes base pages (e.g.
> dax_lock_page()).  For pagemap with compound pages fetch the
> compound_head in case we are handling a tail page memory failure.
>
> Currently this is a nop, but in the advent of compound pages in
> dev_pagemap it allows memory_failure_dev_pagemap() to keep working.
>
> Reported-by: Jane Chu <jane.chu@oracle.com>
> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
> ---
>  mm/memory-failure.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 24210c9bd843..94240d772623 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1318,6 +1318,8 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
>                 goto out;
>         }
>
> +       page = compound_head(page);

Unless / until we do compound pages for the filesystem-dax case, I
would add a comment like:

/* pages instantiated by device-dax (not filesystem-dax) may be
compound pages */