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Howlett" To: Anthony Yznaga Cc: linux-mm@kvack.org, akpm@linux-foundation.org, andreyknvl@gmail.com, arnd@arndb.de, bp@alien8.de, brauner@kernel.org, bsegall@google.com, corbet@lwn.net, dave.hansen@linux.intel.com, david@redhat.com, dietmar.eggemann@arm.com, ebiederm@xmission.com, hpa@zytor.com, jakub.wartak@mailbox.org, jannh@google.com, juri.lelli@redhat.com, khalid@kernel.org, linyongting@bytedance.com, lorenzo.stoakes@oracle.com, luto@kernel.org, markhemm@googlemail.com, maz@kernel.org, mhiramat@kernel.org, mgorman@suse.de, mhocko@suse.com, mingo@redhat.com, muchun.song@linux.dev, neilb@suse.de, osalvador@suse.de, pcc@google.com, peterz@infradead.org, pfalcato@suse.de, rostedt@goodmis.org, rppt@kernel.org, shakeel.butt@linux.dev, surenb@google.com, tglx@linutronix.de, vasily.averin@linux.dev, vbabka@suse.cz, vincent.guittot@linaro.org, viro@zeniv.linux.org.uk, vschneid@redhat.com, willy@infradead.org, x86@kernel.org, xhao@linux.alibaba.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org Subject: Re: [PATCH v3 01/22] mm: Add msharefs filesystem Message-ID: Mail-Followup-To: "Liam R. Howlett" , Anthony Yznaga , linux-mm@kvack.org, akpm@linux-foundation.org, andreyknvl@gmail.com, arnd@arndb.de, bp@alien8.de, brauner@kernel.org, bsegall@google.com, corbet@lwn.net, dave.hansen@linux.intel.com, david@redhat.com, dietmar.eggemann@arm.com, ebiederm@xmission.com, hpa@zytor.com, jakub.wartak@mailbox.org, jannh@google.com, juri.lelli@redhat.com, khalid@kernel.org, linyongting@bytedance.com, lorenzo.stoakes@oracle.com, luto@kernel.org, markhemm@googlemail.com, maz@kernel.org, mhiramat@kernel.org, mgorman@suse.de, mhocko@suse.com, mingo@redhat.com, muchun.song@linux.dev, neilb@suse.de, osalvador@suse.de, pcc@google.com, peterz@infradead.org, pfalcato@suse.de, rostedt@goodmis.org, rppt@kernel.org, shakeel.butt@linux.dev, surenb@google.com, tglx@linutronix.de, vasily.averin@linux.dev, vbabka@suse.cz, vincent.guittot@linaro.org, viro@zeniv.linux.org.uk, vschneid@redhat.com, willy@infradead.org, x86@kernel.org, xhao@linux.alibaba.com, linux-doc@vger.kernel.org, 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List-Unsubscribe: * Anthony Yznaga [250819 21:04]: > From: Khalid Aziz > > Add a pseudo filesystem that contains files and page table sharing > information that enables processes to share page table entries. > 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 | 11 +++ > mm/Makefile | 4 ++ > mm/mshare.c | 97 ++++++++++++++++++++++++++ > 6 files changed, 210 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 11a599387266..dcd6605eb228 100644 > --- a/Documentation/filesystems/index.rst > +++ b/Documentation/filesystems/index.rst > @@ -102,6 +102,7 @@ Documentation for filesystem implementations. > fuse-passthrough > 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 4108bcd96784..8b50e9785729 100644 > --- a/mm/Kconfig > +++ b/mm/Kconfig > @@ -1400,6 +1400,17 @@ config PT_RECLAIM > config FIND_NORMAL_PAGE > def_bool n > > +config MSHARE > + bool "Mshare" > + depends on MMU > + help > + Enable msharefs: A pseudo filesystem that allows multiple processes > + to share kernel resources for mapping shared pages. A file created on > + msharefs represents a shared region where all processes mapping that > + region will map objects within it with shared page table entries and > + VMAs. Ioctls are used to configure and map objects into the shared > + region. > + > source "mm/damon/Kconfig" > > endmenu > diff --git a/mm/Makefile b/mm/Makefile > index ef54aa615d9d..4af111b29c68 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 Probably needs a new year or year range and another author? > + * > + */ > + > +#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; I don't know the recovery here, but what about inode and inode link count? > + > + 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); > -- > 2.47.1 >