The patch titled
Subject: mm/shmem: add hugetlbfs support to memfd_create()
has been added to the -mm tree. Its filename is
mm-shmem-add-hugetlbfs-support-to-memfd_create.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-shmem-add-hugetlbfs-support-to-memfd_create.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-shmem-add-hugetlbfs-support-to-memfd_create.patch
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------------------------------------------------------
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
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.
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>
---
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
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