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This patch adds the basic filesystem that can be mounted, a CONFIG_MSHARE option to enable the feature, and documentation. Signed-off-by: Khalid Aziz Signed-off-by: Anthony Yznaga --- Documentation/filesystems/index.rst | 1 + Documentation/filesystems/msharefs.rst | 96 +++++++++++++++++++++++++ include/uapi/linux/magic.h | 1 + mm/Kconfig | 9 +++ mm/Makefile | 4 ++ mm/mshare.c | 97 ++++++++++++++++++++++++++ 6 files changed, 208 insertions(+) create mode 100644 Documentation/filesystems/msharefs.rst create mode 100644 mm/mshare.c diff --git a/Documentation/filesystems/index.rst b/Documentation/filesystems/index.rst index a9cf8e950b15..573d7a05dbca 100644 --- a/Documentation/filesystems/index.rst +++ b/Documentation/filesystems/index.rst @@ -101,6 +101,7 @@ Documentation for filesystem implementations. fuse-io-uring inotify isofs + msharefs nilfs2 nfs/index ntfs3 diff --git a/Documentation/filesystems/msharefs.rst b/Documentation/filesystems/msharefs.rst new file mode 100644 index 000000000000..3e5b7d531821 --- /dev/null +++ b/Documentation/filesystems/msharefs.rst @@ -0,0 +1,96 @@ +.. SPDX-License-Identifier: GPL-2.0 + +===================================================== +Msharefs - A filesystem to support shared page tables +===================================================== + +What is msharefs? +----------------- + +msharefs is a pseudo filesystem that allows multiple processes to +share page table entries for shared pages. To enable support for +msharefs the kernel must be compiled with CONFIG_MSHARE set. + +msharefs is typically mounted like this:: + + mount -t msharefs none /sys/fs/mshare + +A file created on msharefs creates a new shared region where all +processes mapping that region will map it using shared page table +entries. Once the size of the region has been established via +ftruncate() or fallocate(), the region can be mapped into processes +and ioctls used to map and unmap objects within it. Note that an +msharefs file is a control file and accessing mapped objects within +a shared region through read or write of the file is not permitted. + +How to use mshare +----------------- + +Here are the basic steps for using mshare: + + 1. Mount msharefs on /sys/fs/mshare:: + + mount -t msharefs msharefs /sys/fs/mshare + + 2. mshare regions have alignment and size requirements. Start + address for the region must be aligned to an address boundary and + be a multiple of fixed size. This alignment and size requirement + can be obtained by reading the file ``/sys/fs/mshare/mshare_info`` + which returns a number in text format. mshare regions must be + aligned to this boundary and be a multiple of this size. + + 3. For the process creating an mshare region: + + a. Create a file on /sys/fs/mshare, for example:: + + fd = open("/sys/fs/mshare/shareme", + O_RDWR|O_CREAT|O_EXCL, 0600); + + b. Establish the size of the region:: + + fallocate(fd, 0, 0, BUF_SIZE); + + or:: + + ftruncate(fd, BUF_SIZE); + + c. Map some memory in the region:: + + struct mshare_create mcreate; + + mcreate.region_offset = 0; + mcreate.size = BUF_SIZE; + mcreate.offset = 0; + mcreate.prot = PROT_READ | PROT_WRITE; + mcreate.flags = MAP_ANONYMOUS | MAP_SHARED | MAP_FIXED; + mcreate.fd = -1; + + ioctl(fd, MSHAREFS_CREATE_MAPPING, &mcreate); + + d. Map the mshare region into the process:: + + mmap(NULL, BUF_SIZE, + PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); + + e. Write and read to mshared region normally. + + + 4. For processes attaching an mshare region: + + a. Open the msharefs file, for example:: + + fd = open("/sys/fs/mshare/shareme", O_RDWR); + + b. Get the size of the mshare region from the file:: + + fstat(fd, &sb); + mshare_size = sb.st_size; + + c. Map the mshare region into the process:: + + mmap(NULL, mshare_size, + PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); + + 5. To delete the mshare region:: + + unlink("/sys/fs/mshare/shareme"); diff --git a/include/uapi/linux/magic.h b/include/uapi/linux/magic.h index bb575f3ab45e..e53dd6063cba 100644 --- a/include/uapi/linux/magic.h +++ b/include/uapi/linux/magic.h @@ -103,5 +103,6 @@ #define DEVMEM_MAGIC 0x454d444d /* "DMEM" */ #define SECRETMEM_MAGIC 0x5345434d /* "SECM" */ #define PID_FS_MAGIC 0x50494446 /* "PIDF" */ +#define MSHARE_MAGIC 0x4d534852 /* "MSHR" */ #endif /* __LINUX_MAGIC_H__ */ diff --git a/mm/Kconfig b/mm/Kconfig index d3fb3762887b..e6c90db83d01 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -1342,6 +1342,15 @@ config PT_RECLAIM Note: now only empty user PTE page table pages will be reclaimed. +config MSHARE + bool "Mshare" + depends on MMU + help + Enable msharefs: A ram-based filesystem that allows multiple + processes to share page table entries for shared pages. A file + created on msharefs represents a shared region where all processes + mapping that region will map objects within it with shared PTEs. + Ioctls are used to configure and map objects into the shared region. source "mm/damon/Kconfig" diff --git a/mm/Makefile b/mm/Makefile index e7f6bbf8ae5f..b32aad62589b 100644 --- a/mm/Makefile +++ b/mm/Makefile @@ -48,6 +48,10 @@ ifdef CONFIG_64BIT mmu-$(CONFIG_MMU) += mseal.o endif +ifdef CONFIG_MSHARE +mmu-$(CONFIG_MMU) += mshare.o +endif + obj-y := filemap.o mempool.o oom_kill.o fadvise.o \ maccess.o page-writeback.o folio-compat.o \ readahead.o swap.o truncate.o vmscan.o shrinker.o \ diff --git a/mm/mshare.c b/mm/mshare.c new file mode 100644 index 000000000000..f703af49ec81 --- /dev/null +++ b/mm/mshare.c @@ -0,0 +1,97 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Enable cooperating processes to share page table between + * them to reduce the extra memory consumed by multiple copies + * of page tables. + * + * This code adds an in-memory filesystem - msharefs. + * msharefs is used to manage page table sharing + * + * + * Copyright (C) 2024 Oracle Corp. All rights reserved. + * Author: Khalid Aziz + * + */ + +#include +#include +#include + +static const struct file_operations msharefs_file_operations = { + .open = simple_open, +}; + +static const struct super_operations mshare_s_ops = { + .statfs = simple_statfs, +}; + +static int +msharefs_fill_super(struct super_block *sb, struct fs_context *fc) +{ + struct inode *inode; + + sb->s_blocksize = PAGE_SIZE; + sb->s_blocksize_bits = PAGE_SHIFT; + sb->s_maxbytes = MAX_LFS_FILESIZE; + sb->s_magic = MSHARE_MAGIC; + sb->s_op = &mshare_s_ops; + sb->s_time_gran = 1; + + inode = new_inode(sb); + if (!inode) + return -ENOMEM; + + inode->i_ino = 1; + inode->i_mode = S_IFDIR | 0777; + simple_inode_init_ts(inode); + inode->i_op = &simple_dir_inode_operations; + inode->i_fop = &simple_dir_operations; + set_nlink(inode, 2); + + sb->s_root = d_make_root(inode); + if (!sb->s_root) + return -ENOMEM; + + return 0; +} + +static int +msharefs_get_tree(struct fs_context *fc) +{ + return get_tree_nodev(fc, msharefs_fill_super); +} + +static const struct fs_context_operations msharefs_context_ops = { + .get_tree = msharefs_get_tree, +}; + +static int +mshare_init_fs_context(struct fs_context *fc) +{ + fc->ops = &msharefs_context_ops; + return 0; +} + +static struct file_system_type mshare_fs = { + .name = "msharefs", + .init_fs_context = mshare_init_fs_context, + .kill_sb = kill_litter_super, +}; + +static int __init +mshare_init(void) +{ + int ret; + + ret = sysfs_create_mount_point(fs_kobj, "mshare"); + if (ret) + return ret; + + ret = register_filesystem(&mshare_fs); + if (ret) + sysfs_remove_mount_point(fs_kobj, "mshare"); + + return ret; +} + +core_initcall(mshare_init); -- 2.43.5