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

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Date:   Tue, 1 Aug 2017 10:57:59 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, Matthew Wilcox <willy@...radead.org>,
        akpm@...ux-foundation.org, ak@...ux.intel.com,
        mtk.manpages@...il.com, Davidlohr Bueso <dbueso@...e.de>,
        khandual@...ux.vnet.ibm.com, aneesh.kumar@...ux.vnet.ibm.com,
        aarcange@...hat.com, Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH 1/3] mm:hugetlb: Define system call hugetlb size
 encodings in single file

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@...cle.com>

Acked-by: Michal Hocko <mhocko@...e.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