Re: [PATCH 1/3] mm:hugetlb: Define system call hugetlb size encodings in single file

Michal Hocko
2017-08-01T08:58:02Z

On Mon 31-07-17 11:56:24, Mike Kravetz wrote:
> If hugetlb pages are requested in mmap or shmget system calls, a huge
> page size other than default can be requested. This is accomplished by
> encoding the log2 of the huge page size in the upper bits of the flag
> argument. asm-generic and arch specific headers all define the same
> values for these encodings.
>
> Put common definitions in a single header file. The primary uapi
> header files for mmap and shm will use these definitions as a basis
> for definitions specific to those system calls.
>
> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
> include/uapi/asm-generic/hugetlb_encode.h | 34 +++++++++++++++++++++++++++++++
> 1 file changed, 34 insertions(+)
> create mode 100644 include/uapi/asm-generic/hugetlb_encode.h
>
> diff --git a/include/uapi/asm-generic/hugetlb_encode.h b/include/uapi/asm-generic/hugetlb_encode.h
> new file mode 100644
> index 0000000..e4732d3
> --- /dev/null
> +++ b/include/uapi/asm-generic/hugetlb_encode.h
> @@ -0,0 +1,34 @@
> +#ifndef _ASM_GENERIC_HUGETLB_ENCODE_H_
> +#define _ASM_GENERIC_HUGETLB_ENCODE_H_
> +
> +/*
> + * Several system calls take a flag to request "hugetlb" huge pages.
> + * Without further specification, these system calls will use the
> + * system's default huge page size. If a system supports multiple
> + * huge page sizes, the desired huge page size can be specified in
> + * bits [26:31] of the flag arguments. The value in these 6 bits
> + * will encode the log2 of the huge page size.
> + *
> + * The following definitions are associated with this huge page size
> + * encoding in flag arguments. System call specific header files
> + * that use this encoding should include this file. They can then
> + * provide definitions based on these with their own specific prefix.
> + * for example:
> + * #define MAP_HUGE_SHIFT HUGETLB_FLAG_ENCODE_SHIFT
> + */
> +
> +#define HUGETLB_FLAG_ENCODE_SHIFT 26
> +#define HUGETLB_FLAG_ENCODE_MASK 0x3f
> +
> +#define HUGETLB_FLAG_ENCODE_64KB (16 << HUGETLB_FLAG_ENCODE_SHIFT)
> +#define HUGETLB_FLAG_ENCODE_512KB (19 << HUGETLB_FLAG_ENCODE_SHIFT)
> +#define HUGETLB_FLAG_ENCODE_1MB (20 << HUGETLB_FLAG_ENCODE_SHIFT)
> +#define HUGETLB_FLAG_ENCODE_2MB (21 << HUGETLB_FLAG_ENCODE_SHIFT)
> +#define HUGETLB_FLAG_ENCODE_8MB (23 << HUGETLB_FLAG_ENCODE_SHIFT)
> +#define HUGETLB_FLAG_ENCODE_16MB (24 << HUGETLB_FLAG_ENCODE_SHIFT)
> +#define HUGETLB_FLAG_ENCODE_256MB (28 << HUGETLB_FLAG_ENCODE_SHIFT)
> +#define HUGETLB_FLAG_ENCODE_1GB (30 << HUGETLB_FLAG_ENCODE_SHIFT)
> +#define HUGETLB_FLAG_ENCODE_2GB (31 << HUGETLB_FLAG_ENCODE_SHIFT)
> +#define HUGETLB_FLAG_ENCODE_16GB (34 << HUGETLB_FLAG_ENCODE_SHIFT)
> +
> +#endif /* _ASM_GENERIC_HUGETLB_ENCODE_H_ */
> --
> 2.7.5

--
Michal Hocko
SUSE Labs