Re: + mm-shmem-add-hugetlbfs-support-to-memfd_create.patch added to -mm tree

[Michal Hocko]

[The updated changelog is here so let me comment here]

On Tue 08-08-17 16:19:45, Andrew Morton wrote:
> From: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> Subject: mm/shmem: add hugetlbfs support to memfd_create()
> 
> This patch came out of discussions in this e-mail thread:
> https://lkml.org/lkml/2017/7/6/564

Use
http://lkml.kernel.org/r/1499357846-7481-1-git-send-email-mike.kravetz%40oracle.com
instead please. lkml.org is broken quite often

> The Oracle JVM team is developing a new garbage collection model.  This
> new model requires multiple mappings of the same anonymous memory.  One
> straightforward way to accomplish this is with memfd_create.  They can use
> the returned fd to create multiple mappings of the same memory.
> 
> The JVM today has an option to use (static hugetlb) huge pages.  If this
> option is specified, they would like to use the same garbage collection
> model requiring multiple mappings to the same memory.  Using hugetlbfs, it
> is possible to explicitly mount a filesystem and specify file paths in
> order to get an fd that can be used for multiple mappings.  However, this
> introduces additional system admin work and coordination.
> 
> Ideally they would like to get a hugetlbfs fd without requiring explicit
> mounting of a filesystem.  Today, mmap and shmget can make use of
> hugetlbfs without explicitly mounting a filesystem.  The patch adds this
> functionality to hugetlbfs.
> 
> A new flag MFD_HUGETLB is introduced to request a hugetlbfs file.  Like
> other system calls where hugetlb can be requested, the huge page size can
> be encoded in the flags argument is the non-default huge page size is
> desired.  hugetlbfs does not support sealing operations, therefore
> specifying MFD_ALLOW_SEALING with MFD_HUGETLB will result in EINVAL.
> 
> Of course, the memfd_man page would need updating if this type of
> functionality moves forward.
> 
> 
> Add a new flag MFD_HUGETLB to memfd_create() that will specify the file to
> be created resides in the hugetlbfs filesystem.  This is the generic
> hugetlbfs filesystem not associated with any specific mount point.  As
> with other system calls that request hugetlbfs backed pages, there is the
> ability to encode huge page size in the flag arguments.
> 
> hugetlbfs does not support sealing operations, therefore specifying
> MFD_ALLOW_SEALING with MFD_HUGETLB will result in EINVAL.

last two paragraphs are duplicated so they can be dropped

> Link: http://lkml.kernel.org/r/1502149672-7759-2-git-send-email-mike.kravetz@xxxxxxxxxx
> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
> Cc: "Kirill A . Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>

Other than that it looks reasonably to me.
Acked-by: Michal Hocko <mhocko@xxxxxxxx>

> ---
> 
>  include/uapi/linux/memfd.h |   24 ++++++++++++++++++++++
>  mm/shmem.c                 |   37 +++++++++++++++++++++++++++++------
>  2 files changed, 55 insertions(+), 6 deletions(-)
> 
> diff -puN include/uapi/linux/memfd.h~mm-shmem-add-hugetlbfs-support-to-memfd_create include/uapi/linux/memfd.h
> --- a/include/uapi/linux/memfd.h~mm-shmem-add-hugetlbfs-support-to-memfd_create
> +++ a/include/uapi/linux/memfd.h
> @@ -1,8 +1,32 @@
>  #ifndef _UAPI_LINUX_MEMFD_H
>  #define _UAPI_LINUX_MEMFD_H
>  
> +#include <asm-generic/hugetlb_encode.h>
> +
>  /* flags for memfd_create(2) (unsigned int) */
>  #define MFD_CLOEXEC		0x0001U
>  #define MFD_ALLOW_SEALING	0x0002U
> +#define MFD_HUGETLB		0x0004U
> +
> +/*
> + * Huge page size encoding when MFD_HUGETLB is specified, and a huge page
> + * size other than the default is desired.  See hugetlb_encode.h.
> + * All known huge page size encodings are provided here.  It is the
> + * responsibility of the application to know which sizes are supported on
> + * the running system.  See mmap(2) man page for details.
> + */
> +#define MFD_HUGE_SHIFT	HUGETLB_FLAG_ENCODE_SHIFT
> +#define MFD_HUGE_MASK	HUGETLB_FLAG_ENCODE_MASK
> +
> +#define MFD_HUGE_64KB	HUGETLB_FLAG_ENCODE_64KB
> +#define MFD_HUGE_512KB	HUGETLB_FLAG_ENCODE_512KB
> +#define MFD_HUGE_1MB	HUGETLB_FLAG_ENCODE_1MB
> +#define MFD_HUGE_2MB	HUGETLB_FLAG_ENCODE_2MB
> +#define MFD_HUGE_8MB	HUGETLB_FLAG_ENCODE_8MB
> +#define MFD_HUGE_16MB	HUGETLB_FLAG_ENCODE_16MB
> +#define MFD_HUGE_256MB	HUGETLB_FLAG_ENCODE_256MB
> +#define MFD_HUGE_1GB	HUGETLB_FLAG_ENCODE_1GB
> +#define MFD_HUGE_2GB	HUGETLB_FLAG_ENCODE_2GB
> +#define MFD_HUGE_16GB	HUGETLB_FLAG_ENCODE_16GB
>  
>  #endif /* _UAPI_LINUX_MEMFD_H */
> diff -puN mm/shmem.c~mm-shmem-add-hugetlbfs-support-to-memfd_create mm/shmem.c
> --- a/mm/shmem.c~mm-shmem-add-hugetlbfs-support-to-memfd_create
> +++ a/mm/shmem.c
> @@ -34,6 +34,7 @@
>  #include <linux/swap.h>
>  #include <linux/uio.h>
>  #include <linux/khugepaged.h>
> +#include <linux/hugetlb.h>
>  
>  #include <asm/tlbflush.h> /* for arch/microblaze update_mmu_cache() */
>  
> @@ -3652,7 +3653,7 @@ static int shmem_show_options(struct seq
>  #define MFD_NAME_PREFIX_LEN (sizeof(MFD_NAME_PREFIX) - 1)
>  #define MFD_NAME_MAX_LEN (NAME_MAX - MFD_NAME_PREFIX_LEN)
>  
> -#define MFD_ALL_FLAGS (MFD_CLOEXEC | MFD_ALLOW_SEALING)
> +#define MFD_ALL_FLAGS (MFD_CLOEXEC | MFD_ALLOW_SEALING | MFD_HUGETLB)
>  
>  SYSCALL_DEFINE2(memfd_create,
>  		const char __user *, uname,
> @@ -3664,8 +3665,18 @@ SYSCALL_DEFINE2(memfd_create,
>  	char *name;
>  	long len;
>  
> -	if (flags & ~(unsigned int)MFD_ALL_FLAGS)
> -		return -EINVAL;
> +	if (!(flags & MFD_HUGETLB)) {
> +		if (flags & ~(unsigned int)MFD_ALL_FLAGS)
> +			return -EINVAL;
> +	} else {
> +		/* Sealing not supported in hugetlbfs (MFD_HUGETLB) */
> +		if (flags & MFD_ALLOW_SEALING)
> +			return -EINVAL;
> +		/* Allow huge page size encoding in flags. */
> +		if (flags & ~(unsigned int)(MFD_ALL_FLAGS |
> +				(MFD_HUGE_MASK << MFD_HUGE_SHIFT)))
> +			return -EINVAL;
> +	}
>  
>  	/* length includes terminating zero */
>  	len = strnlen_user(uname, MFD_NAME_MAX_LEN + 1);
> @@ -3696,16 +3707,30 @@ SYSCALL_DEFINE2(memfd_create,
>  		goto err_name;
>  	}
>  
> -	file = shmem_file_setup(name, 0, VM_NORESERVE);
> +	if (flags & MFD_HUGETLB) {
> +		struct user_struct *user = NULL;
> +
> +		file = hugetlb_file_setup(name, 0, VM_NORESERVE, &user,
> +					HUGETLB_ANONHUGE_INODE,
> +					(flags >> MFD_HUGE_SHIFT) &
> +					MFD_HUGE_MASK);
> +	} else
> +		file = shmem_file_setup(name, 0, VM_NORESERVE);
>  	if (IS_ERR(file)) {
>  		error = PTR_ERR(file);
>  		goto err_fd;
>  	}
> -	info = SHMEM_I(file_inode(file));
>  	file->f_mode |= FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE;
>  	file->f_flags |= O_RDWR | O_LARGEFILE;
> -	if (flags & MFD_ALLOW_SEALING)
> +
> +	if (flags & MFD_ALLOW_SEALING) {
> +		/*
> +		 * flags check at beginning of function ensures
> +		 * this is not a hugetlbfs (MFD_HUGETLB) file.
> +		 */
> +		info = SHMEM_I(file_inode(file));
>  		info->seals &= ~F_SEAL_SEAL;
> +	}
>  
>  	fd_install(fd, file);
>  	kfree(name);
> _
> 
> Patches currently in -mm which might be from mike.kravetz@xxxxxxxxxx are
> 
> mm-mremap-fail-map-duplication-attempts-for-private-mappings.patch
> mm-hugetlb-define-system-call-hugetlb-size-encodings-in-single-file.patch
> mm-arch-consolidate-mmap-hugetlb-size-encodings.patch
> mm-shm-use-new-hugetlb-size-encoding-definitions.patch
> mm-shmem-add-hugetlbfs-support-to-memfd_create.patch

-- 
Michal Hocko
SUSE Labs