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SubjectRe: [patch] memfd_create.2: Add description of MFD_HUGETLB (hugetlbfs) support
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Hi Mike,

On 09/15/2017 11:43 PM, Mike Kravetz wrote:
> hugetlbfs support for memfd_create was recently merged by Linus and
> should be in the Linux 4.14 release. To request hugetlbfs support
> a new memfd_create flag (MFD_HUGETLB) was added.
>
> This patch documents the following commit:
>
> commit 749df87bd7bee5a79cef073f5d032ddb2b211de8
> Author: Mike Kravetz <mike.kravetz@oracle.com>
> Date: Wed Sep 6 16:24:16 2017 -0700
>
> mm/shmem: add hugetlbfs support to memfd_create()

Thanks! I've applied this patch.

Cheers,

Michael

>
> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
> ---
> man2/memfd_create.2 | 27 +++++++++++++++++++++++++++
> 1 file changed, 27 insertions(+)
>
> diff --git a/man2/memfd_create.2 b/man2/memfd_create.2
> index 4dfd1bb2d..b61254bb8 100644
> --- a/man2/memfd_create.2
> +++ b/man2/memfd_create.2
> @@ -100,6 +100,33 @@ If this flag is not set, the initial set of seals will be
> meaning that no other seals can be set on the file.
> .\" FIXME Why is the MFD_ALLOW_SEALING behavior not simply the default?
> .\" Is it worth adding some text explaining this?
> +.TP
> +.BR MFD_HUGETLB " (since Linux 4.14)"
> +The anonymous file will be created in the hugetlbfs filesystem using
> +huge pages. See the Linux kernel source file
> +.I Documentation/vm/hugetlbpage.txt
> +for more information about hugetlbfs. The hugetlbfs filesystem does
> +not support file sealing operations. Therefore, specifying both
> +.B MFD_HUGETLB
> +and
> +.B MFD_ALLOW_SEALING
> +will result in an error
> +.RB (EINVAL)
> +being returned.
> +
> +.TP
> +.BR MFD_HUGE_2MB ", " MFD_HUGE_1GB ", " "..."
> +Used in conjunction with
> +.B MFD_HUGETLB
> +to select alternative hugetlb page sizes (respectively, 2 MB, 1 GB, ...)
> +on systems that support multiple hugetlb page sizes. Definitions for known
> +huge page sizes are included in the header file
> +.I <sys/memfd.h>.
> +
> +For details on encoding huge page sizes not included in the header file,
> +see the discussion of the similarly named constants in
> +.BR mmap (2).
> +
> .PP
> Unused bits in
> .I flags
>


--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/

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