[099/262] mm/vmalloc: be more explicit about supported gfp flags

Commit Message

Andrew Morton Nov. 5, 2021, 8:39 p.m. UTC

From: Michal Hocko <[e-mail]>
Subject: mm/vmalloc: be more explicit about supported gfp flags

The core of the vmalloc allocator __vmalloc_area_node doesn't say anything
about gfp mask argument.  Not all gfp flags are supported though.  Be more
explicit about constraints.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Michal Hocko <[e-mail]>
Cc: Dave Chinner <[e-mail]>
Cc: Neil Brown <[e-mail]>
Cc: Christoph Hellwig <[e-mail]>
Cc: Uladzislau Rezki <[e-mail]>
Cc: Ilya Dryomov <[e-mail]>
Cc: Jeff Layton <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 mm/vmalloc.c |   12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

Comments

Michal Hocko Nov. 8, 2021, 9:25 a.m. UTC | #1

On Fri 05-11-21 13:39:50, Andrew Morton wrote:
> From: Michal Hocko <[e-mail]>
> Subject: mm/vmalloc: be more explicit about supported gfp flags
> 
> The core of the vmalloc allocator __vmalloc_area_node doesn't say anything
> about gfp mask argument.  Not all gfp flags are supported though.  Be more
> explicit about constraints.
> 
> Link: https://lkml.kernel.org/r/[e-mail]
> Signed-off-by: Michal Hocko <[e-mail]>
> Cc: Dave Chinner <[e-mail]>
> Cc: Neil Brown <[e-mail]>
> Cc: Christoph Hellwig <[e-mail]>
> Cc: Uladzislau Rezki <[e-mail]>
> Cc: Ilya Dryomov <[e-mail]>
> Cc: Jeff Layton <[e-mail]>
> Signed-off-by: Andrew Morton <[e-mail]>

As already pointed out
http://lkml.kernel.org/r/[e-mail] this patch
cannot be applied without other patches from the same series.

> ---
> 
>  mm/vmalloc.c |   12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> --- a/mm/vmalloc.c~mm-vmalloc-be-more-explicit-about-supported-gfp-flags
> +++ a/mm/vmalloc.c
> @@ -2983,8 +2983,16 @@ fail:
>   * @caller:		  caller's return address
>   *
>   * Allocate enough pages to cover @size from the page level
> - * allocator with @gfp_mask flags.  Map them into contiguous
> - * kernel virtual space, using a pagetable protection of @prot.
> + * allocator with @gfp_mask flags. Please note that the full set of gfp
> + * flags are not supported. GFP_KERNEL would be a preferred allocation mode
> + * but GFP_NOFS and GFP_NOIO are supported as well. Zone modifiers are not
> + * supported. From the reclaim modifiers__GFP_DIRECT_RECLAIM is required (aka
> + * GFP_NOWAIT is not supported) and only __GFP_NOFAIL is supported (aka
> + * __GFP_NORETRY and __GFP_RETRY_MAYFAIL are not supported).
> + * __GFP_NOWARN can be used to suppress error messages about failures.
> + *
> + * Map them into contiguous kernel virtual space, using a pagetable
> + * protection of @prot.
>   *
>   * Return: the address of the area or %NULL on failure
>   */
> _

Linus Torvalds Nov. 8, 2021, 5:15 p.m. UTC | #2

On Mon, Nov 8, 2021 at 1:25 AM Michal Hocko <[e-mail]> wrote:
>
> As already pointed out
> http://lkml.kernel.org/r/[e-mail] this patch
> cannot be applied without other patches from the same series.

Hmm. I've taken it already.

Not a huge deal, since it's a comment change - and the code will
presumably eventually match the updated comment.

I guess it's a new thing that instead of stale comments, we have
future-proof ones ;)

              Linus

Michal Hocko Nov. 8, 2021, 5:30 p.m. UTC | #3

On Mon 08-11-21 09:15:04, Linus Torvalds wrote:
> On Mon, Nov 8, 2021 at 1:25 AM Michal Hocko <[e-mail]> wrote:
> >
> > As already pointed out
> > http://lkml.kernel.org/r/[e-mail] this patch
> > cannot be applied without other patches from the same series.
> 
> Hmm. I've taken it already.
> 
> Not a huge deal, since it's a comment change - and the code will
> presumably eventually match the updated comment.

I plan to send the rest after the merge window.
 
> I guess it's a new thing that instead of stale comments, we have
> future-proof ones ;)

I just hope nobody gets confused about which are not supported yet. E.g.
GFP_NOFAIL, GFP_NO{FS,IO}. In both cases the direct use could lead to
bugs.

Patch

--- a/mm/vmalloc.c~mm-vmalloc-be-more-explicit-about-supported-gfp-flags
+++ a/mm/vmalloc.c
@@ -2983,8 +2983,16 @@  fail:
  * @caller:		  caller's return address
  *
  * Allocate enough pages to cover @size from the page level
- * allocator with @gfp_mask flags.  Map them into contiguous
- * kernel virtual space, using a pagetable protection of @prot.
+ * allocator with @gfp_mask flags. Please note that the full set of gfp
+ * flags are not supported. GFP_KERNEL would be a preferred allocation mode
+ * but GFP_NOFS and GFP_NOIO are supported as well. Zone modifiers are not
+ * supported. From the reclaim modifiers__GFP_DIRECT_RECLAIM is required (aka
+ * GFP_NOWAIT is not supported) and only __GFP_NOFAIL is supported (aka
+ * __GFP_NORETRY and __GFP_RETRY_MAYFAIL are not supported).
+ * __GFP_NOWARN can be used to suppress error messages about failures.
+ *
+ * Map them into contiguous kernel virtual space, using a pagetable
+ * protection of @prot.
  *
  * Return: the address of the area or %NULL on failure
  */