From nobody Mon Feb 9 14:32:53 2026 Received: from mx0a-00069f02.pphosted.com (mx0a-00069f02.pphosted.com [205.220.165.32]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 29BF213CA9C; Fri, 4 Apr 2025 02:19:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=205.220.165.32 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743733199; cv=none; b=la4gdxq8Hb1pibdyBTv9tA/SnVK/h52pvgL59mCq5H3juIEJmiEd1yKhmfGuj3jrCBpAKtKt1Nyvg1mvS/mwB2rm1xU5xZh4k4b4CqOK+y/L8drEK3hgU9oaEJX4cQ/vGSod7k2IWz7s9zWrKR+hGSgK2lkRNaEhxCmIIXNB+pE= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743733199; c=relaxed/simple; bh=SiyoxJ1X5XIAgrXKDBaL/qBu+xpWd/HBVR17s0PrL6k=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=skfppGDHKgCLTbn/xwNFJ8jL1u9u2ZPHmvihdkp7iEGMQ1qsCqSTDF8uSIeumIqpWL5Bj1gAvnkSbStiE4uf+Q2aHjY6dshdD7jFOLIl+W3dApbeGqMVeRYGgw57UWLShbxDJb1Plqzmn7ATs7Orb3s6/SDCWUSbX+OLE8f96vg= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=oracle.com; spf=pass smtp.mailfrom=oracle.com; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b=ZfgPtYYp; arc=none smtp.client-ip=205.220.165.32 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=oracle.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=oracle.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="ZfgPtYYp" Received: from pps.filterd (m0333521.ppops.net [127.0.0.1]) by mx0b-00069f02.pphosted.com (8.18.1.2/8.18.1.2) with ESMTP id 5341N2KW003850; Fri, 4 Apr 2025 02:19:10 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=cc :content-transfer-encoding:date:from:in-reply-to:message-id :mime-version:references:subject:to; s=corp-2023-11-20; bh=s3Be4 h3gS8mZLGO0ggl9ZrqQVZS1VM6QgX8fGTsPeZ0=; b=ZfgPtYYpoylzoJBqsSQeN LUYLNPEY9WvV+15bBaK2cB95PXsUxqWAXwZmbBT/XnmmN/N5zvfkQQ//334Y4a6w 5B0GtTjwvqIizjHEbdwyhiMvk4+uHdw90DHrzc/jOOv/3m7rxJ8yrpo2loCL1xFK PqtQcQz/DhjIMuYJsR6M3LRxQam9nSH6drJw9VyZl2WuXTU1QzkYKBrrpKsp3SPm MHVQYHHxUBNEA0vKQCsEG8gRKyChBbmmWhyw+YDQyU53+D3Cf0jea5XhXTPEgHzg lrBNzCH+KF50lCO1XMHs4dx5a1UkrdPqt/YXt0IIMFCxowfsem9GCj5Te+4aimnM g== Received: from iadpaimrmta02.imrmtpd1.prodappiadaev1.oraclevcn.com (iadpaimrmta02.appoci.oracle.com [147.154.18.20]) by mx0b-00069f02.pphosted.com (PPS) with ESMTPS id 45p7sax3x5-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 04 Apr 2025 02:19:09 +0000 (GMT) Received: from pps.filterd (iadpaimrmta02.imrmtpd1.prodappiadaev1.oraclevcn.com [127.0.0.1]) by iadpaimrmta02.imrmtpd1.prodappiadaev1.oraclevcn.com (8.18.1.2/8.18.1.2) with ESMTP id 5340fjJl017569; Fri, 4 Apr 2025 02:19:08 GMT Received: from pps.reinject (localhost [127.0.0.1]) by iadpaimrmta02.imrmtpd1.prodappiadaev1.oraclevcn.com (PPS) with ESMTPS id 45t2pspj8d-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 04 Apr 2025 02:19:08 +0000 Received: from iadpaimrmta02.imrmtpd1.prodappiadaev1.oraclevcn.com (iadpaimrmta02.imrmtpd1.prodappiadaev1.oraclevcn.com [127.0.0.1]) by pps.reinject (8.17.1.5/8.17.1.5) with ESMTP id 5342H8gc030074; Fri, 4 Apr 2025 02:19:07 GMT Received: from localhost.localdomain (ca-dev60.us.oracle.com [10.129.136.27]) by iadpaimrmta02.imrmtpd1.prodappiadaev1.oraclevcn.com (PPS) with ESMTP id 45t2pspj73-2; Fri, 04 Apr 2025 02:19:07 +0000 From: Anthony Yznaga To: akpm@linux-foundation.org, willy@infradead.org, markhemm@googlemail.com, viro@zeniv.linux.org.uk, david@redhat.com, khalid@kernel.org Cc: anthony.yznaga@oracle.com, andreyknvl@gmail.com, dave.hansen@intel.com, luto@kernel.org, brauner@kernel.org, arnd@arndb.de, ebiederm@xmission.com, catalin.marinas@arm.com, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mhiramat@kernel.org, rostedt@goodmis.org, vasily.averin@linux.dev, xhao@linux.alibaba.com, pcc@google.com, neilb@suse.de, maz@kernel.org Subject: [PATCH v2 01/20] mm: Add msharefs filesystem Date: Thu, 3 Apr 2025 19:18:43 -0700 Message-ID: <20250404021902.48863-2-anthony.yznaga@oracle.com> X-Mailer: git-send-email 2.43.5 In-Reply-To: <20250404021902.48863-1-anthony.yznaga@oracle.com> References: <20250404021902.48863-1-anthony.yznaga@oracle.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1095,Hydra:6.0.680,FMLib:17.12.68.34 definitions=2025-04-04_01,2025-04-03_03,2024-11-22_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 phishscore=0 bulkscore=0 mlxscore=0 spamscore=0 adultscore=0 suspectscore=0 mlxlogscore=999 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2502280000 definitions=main-2504040014 X-Proofpoint-GUID: idsw14QBE2ePZgxGjKQz5K2iLCV9N4Lh X-Proofpoint-ORIG-GUID: idsw14QBE2ePZgxGjKQz5K2iLCV9N4Lh Content-Type: text/plain; charset="utf-8" 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 | 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/filesystem= s/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/filesys= tems/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 + +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D +Msharefs - A filesystem to support shared page tables +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D + +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 =3D 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 =3D 0; + mcreate.size =3D BUF_SIZE; + mcreate.offset =3D 0; + mcreate.prot =3D PROT_READ | PROT_WRITE; + mcreate.flags =3D MAP_ANONYMOUS | MAP_SHARED | MAP_FIXED; + mcreate.fd =3D -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 =3D open("/sys/fs/mshare/shareme", O_RDWR); + + b. Get the size of the mshare region from the file:: + + fstat(fd, &sb); + mshare_size =3D 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" */ =20 #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 =20 Note: now only empty user PTE page table pages will be reclaimed. =20 +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. =20 source "mm/damon/Kconfig" =20 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-$(CONFIG_MMU) +=3D mseal.o endif =20 +ifdef CONFIG_MSHARE +mmu-$(CONFIG_MMU) +=3D mshare.o +endif + obj-y :=3D 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 =3D { + .open =3D simple_open, +}; + +static const struct super_operations mshare_s_ops =3D { + .statfs =3D simple_statfs, +}; + +static int +msharefs_fill_super(struct super_block *sb, struct fs_context *fc) +{ + struct inode *inode; + + sb->s_blocksize =3D PAGE_SIZE; + sb->s_blocksize_bits =3D PAGE_SHIFT; + sb->s_maxbytes =3D MAX_LFS_FILESIZE; + sb->s_magic =3D MSHARE_MAGIC; + sb->s_op =3D &mshare_s_ops; + sb->s_time_gran =3D 1; + + inode =3D new_inode(sb); + if (!inode) + return -ENOMEM; + + inode->i_ino =3D 1; + inode->i_mode =3D S_IFDIR | 0777; + simple_inode_init_ts(inode); + inode->i_op =3D &simple_dir_inode_operations; + inode->i_fop =3D &simple_dir_operations; + set_nlink(inode, 2); + + sb->s_root =3D 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 =3D { + .get_tree =3D msharefs_get_tree, +}; + +static int +mshare_init_fs_context(struct fs_context *fc) +{ + fc->ops =3D &msharefs_context_ops; + return 0; +} + +static struct file_system_type mshare_fs =3D { + .name =3D "msharefs", + .init_fs_context =3D mshare_init_fs_context, + .kill_sb =3D kill_litter_super, +}; + +static int __init +mshare_init(void) +{ + int ret; + + ret =3D sysfs_create_mount_point(fs_kobj, "mshare"); + if (ret) + return ret; + + ret =3D register_filesystem(&mshare_fs); + if (ret) + sysfs_remove_mount_point(fs_kobj, "mshare"); + + return ret; +} + +core_initcall(mshare_init); --=20 2.43.5