linux-kernel - Re: [PATCH v5 3/5] mm: introduce mmap3 for safely defining new mmap flags

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Date:   Wed, 16 Aug 2017 14:15:41 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     akpm@...ux-foundation.org, Jan Kara <jack@...e.cz>,
        Arnd Bergmann <arnd@...db.de>, linux-nvdimm@...ts.01.org,
        linux-api@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-mm@...ck.org, luto@...nel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v5 3/5] mm: introduce mmap3 for safely defining new mmap
 flags

On Wed, Aug 16, 2017 at 12:44:22AM -0700, Dan Williams wrote:
> diff --git a/include/linux/mman.h b/include/linux/mman.h
> index c8367041fafd..0e1de42c836f 100644
> --- a/include/linux/mman.h
> +++ b/include/linux/mman.h
> @@ -7,6 +7,40 @@
>  #include <linux/atomic.h>
>  #include <uapi/linux/mman.h>
>  
> +#ifndef MAP_32BIT
> +#define MAP_32BIT 0
> +#endif
> +#ifndef MAP_HUGE_2MB
> +#define MAP_HUGE_2MB 0
> +#endif
> +#ifndef MAP_HUGE_1GB
> +#define MAP_HUGE_1GB 0
> +#endif
> +
> +/*
> + * The historical set of flags that all mmap implementations implicitly
> + * support when file_operations.mmap_supported_mask is zero.
> + */
> +#define LEGACY_MAP_SUPPORTED_MASK (MAP_SHARED \
> +		| MAP_PRIVATE \
> +		| MAP_FIXED \
> +		| MAP_ANONYMOUS \
> +		| MAP_UNINITIALIZED \
> +		| MAP_GROWSDOWN \
> +		| MAP_DENYWRITE \
> +		| MAP_EXECUTABLE \
> +		| MAP_LOCKED \
> +		| MAP_NORESERVE \
> +		| MAP_POPULATE \
> +		| MAP_NONBLOCK \
> +		| MAP_STACK \
> +		| MAP_HUGETLB \
> +		| MAP_32BIT \
> +		| MAP_HUGE_2MB \
> +		| MAP_HUGE_1GB)
> +
> +#define	MAP_SUPPORTED_MASK (LEGACY_MAP_SUPPORTED_MASK)
> +
>  extern int sysctl_overcommit_memory;
>  extern int sysctl_overcommit_ratio;
>  extern unsigned long sysctl_overcommit_kbytes;

Since we looking into mmap(2) ABI, maybe we should consider re-defining
MAP_DENYWRITE and MAP_EXECUTABLE as 0 in hope that we would be able to
re-use these bits in the future? These flags are ignored now anyway.

-- 
 Kirill A. Shutemov