Re: [PATCH] mm/mremap: Document MREMAP_FIXED dependency on MREMAP_MAYMOVE

From: Michal Hocko
Date: Mon Jul 10 2017 - 09:41:36 EST


On Mon 10-07-17 17:02:11, Anshuman Khandual wrote:
> In the header file, just specify the dependency of MREMAP_FIXED
> on MREMAP_MAYMOVE and make it explicit for the user space.

I really fail to see a point of this patch. The depency belongs to the
code and it seems that we already enforce it
if (flags & MREMAP_FIXED && !(flags & MREMAP_MAYMOVE))
return ret;

So what is the point here?

> Signed-off-by: Anshuman Khandual <khandual@xxxxxxxxxxxxxxxxxx>
> ---
> include/uapi/linux/mman.h | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/include/uapi/linux/mman.h b/include/uapi/linux/mman.h
> index ade4acd..8cae3f6 100644
> --- a/include/uapi/linux/mman.h
> +++ b/include/uapi/linux/mman.h
> @@ -3,8 +3,10 @@
>
> #include <asm/mman.h>
>
> -#define MREMAP_MAYMOVE 1
> -#define MREMAP_FIXED 2
> +#define MREMAP_MAYMOVE 1 /* VMA can move after remap and resize */
> +#define MREMAP_FIXED 2 /* VMA can remap at particular address */
> +
> +/* NOTE: MREMAP_FIXED must be set with MREMAP_MAYMOVE, not alone */
>
> #define OVERCOMMIT_GUESS 0
> #define OVERCOMMIT_ALWAYS 1
> --
> 1.8.5.2
>
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--
Michal Hocko
SUSE Labs