[v6,18/26] mm/gup: Don't allow FOLL_LONGTERM pinning of FS DAX pages

Commit Message

Alistair Popple Jan. 10, 2025, 6 a.m. UTC

Longterm pinning of FS DAX pages should already be disallowed by
various pXX_devmap checks. However a future change will cause these
checks to be invalid for FS DAX pages so make
folio_is_longterm_pinnable() return false for FS DAX pages.

Signed-off-by: Alistair Popple <[e-mail]>
Reviewed-by: John Hubbard <[e-mail]>
Acked-by: David Hildenbrand <[e-mail]>
---
 include/linux/mm.h | 4 ++++
 1 file changed, 4 insertions(+)

Comments

Dan Williams Jan. 14, 2025, 2:16 a.m. UTC | #1

Alistair Popple wrote:
> Longterm pinning of FS DAX pages should already be disallowed by
> various pXX_devmap checks. However a future change will cause these
> checks to be invalid for FS DAX pages so make
> folio_is_longterm_pinnable() return false for FS DAX pages.
> 
> Signed-off-by: Alistair Popple <[e-mail]>
> Reviewed-by: John Hubbard <[e-mail]>
> Acked-by: David Hildenbrand <[e-mail]>
> ---
>  include/linux/mm.h | 4 ++++
>  1 file changed, 4 insertions(+)

> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index f267b06..01edca9 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2078,6 +2078,10 @@ static inline bool folio_is_longterm_pinnable(struct folio *folio)
>  	if (folio_is_device_coherent(folio))
>  		return false;
>  
> +	/* DAX must also always allow eviction. */

This 'eviction' terminology seems like it was copied from the
device-memory comment, but with fsdax it does not fit. How about:

/*
 * Filesystems can only tolerate transient delays to truncate and
 * hole-punch operations
 */

> +	if (folio_is_fsdax(folio))
> +		return false;
> +

After the comment fixup you can add:

Reviewed-by: Dan Williams <[e-mail]>

Patch

diff --git a/include/linux/mm.h b/include/linux/mm.h
index f267b06..01edca9 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2078,6 +2078,10 @@  static inline bool folio_is_longterm_pinnable(struct folio *folio)
 	if (folio_is_device_coherent(folio))
 		return false;
 
+	/* DAX must also always allow eviction. */
+	if (folio_is_fsdax(folio))
+		return false;
+
 	/* Otherwise, non-movable zone folios can be pinned. */
 	return !folio_is_zone_movable(folio);