Re: [PATCH 04/22] mm: don't clear ->mapping in hmm_devmem_free

[John Hubbard]

On 6/13/19 2:43 AM, Christoph Hellwig wrote:
> ->mapping isn't even used by HMM users, and the field at the same offset
> in the zone_device part of the union is declared as pad.  (Which btw is
> rather confusing, as DAX uses ->pgmap and ->mapping from two different
> sides of the union, but DAX doesn't use hmm_devmem_free).
> 
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
>  mm/hmm.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/mm/hmm.c b/mm/hmm.c
> index 0c62426d1257..e1dc98407e7b 100644
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -1347,8 +1347,6 @@ static void hmm_devmem_free(struct page *page, void *data)
>  {
>  	struct hmm_devmem *devmem = data;
>  
> -	page->mapping = NULL;
> -
>  	devmem->ops->free(devmem, page);
>  }
>  
> 

Yes, I think that line was unnecessary. I see from git history that it was
originally being set to NULL from within __put_devmap_managed_page(), and then
in commit 2fa147bdbf672c53386a8f5f2c7fe358004c3ef8, Dan moved it out of there,
and stashed in specifically here. But it appears to have been unnecessary from
the beginning.

Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx> 

thanks,
-- 
John Hubbard
NVIDIA