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Wong" , Randy Dunlap , Jeff Layton , Amir Goldstein , Jonathan Cameron , Stefan Hajnoczi , Joanne Koong , Josef Bacik , Bagas Sanjaya , Chen Linxuan , James Morse , Fuad Tabba , Sean Christopherson , Shivank Garg , Ackerley Tng , Gregory Price , Aravind Ramesh , Ajay Joshi , venkataravis@micron.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, nvdimm@lists.linux.dev, linux-cxl@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: [PATCH BUNDLE] famfs: Fabric-Attached Memory File System Date: Wed, 7 Jan 2026 09:32:44 -0600 Message-ID: <20260107153244.64703-1-john@groves.net> X-Mailer: git-send-email 2.50.1 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit This is a coordinated patch submission for famfs (Fabric-Attached Memory File System) across three repositories: 1. Linux kernel (21 patches) - dax fsdev driver + fuse/famfs integration 2. libfuse (4 patches) - famfs protocol support for fuse servers 3. ndctl/daxctl (2 patches) - support for the new "famfs" devdax mode Each series is posted as a reply to this cover message, with individual patches replying to their respective series cover. Overview -------- Famfs exposes shared memory as a file system. It consumes shared memory from dax devices and provides memory-mappable files that map directly to the memory with no page cache involvement. Famfs differs from conventional file systems in fs-dax mode in that it handles in-memory metadata in a sharable way (which begins with never caching dirty shared metadata). Famfs started as a standalone file system [1,2], but the consensus at LSFMM 2024 and 2025 [3,4] was that it should be ported into fuse. The key performance requirement is that famfs must resolve mapping faults without upcalls. This is achieved by fully caching the file-to-devdax metadata for all active files via two fuse client/server message/response pairs: GET_FMAP and GET_DAXDEV. Patch Series Summary -------------------- Linux Kernel (V3, 21 patches): - dax: New fsdev driver (drivers/dax/fsdev.c) providing a devdax mode compatible with fs-dax. Devices can be switched among 'devdax', 'fsdev' and 'system-ram' modes via daxctl or sysfs. - fuse: Famfs integration adding GET_FMAP and GET_DAXDEV messages for caching file-to-dax mappings in the kernel. libfuse (V2, 4 patches): - Updates fuse_kernel.h to kernel 6.19 baseline - Adds famfs DAX fmap protocol definitions - Adds API for kernel mount options - Implements famfs DAX fmap support for fuse servers ndctl/daxctl (2 patches): - Adds daxctl support for the new "famfs" mode of devdax - Adds test/daxctl-famfs.sh for testing mode transitions Changes Since V2 (kernel) ------------------------- - Dax: Completely new fsdev driver replaces the dev_dax_iomap modifications. Uses MEMORY_DEVICE_FS_DAX type with order-0 folios for fs-dax compatibility. - Dax: The "poisoned page" problem is properly fixed via fsdev_clear_folio_state() which clears stale mapping/compound state when fsdev binds. - Dax: Added dax_set_ops() and driver unbind protection while filesystem mounted. - Fuse: Famfs mounts require CAP_SYS_RAWIO (exposing raw memory devices). - Fuse: Added DAX address_space_operations with noop_dirty_folio. - Rebased to latest kernels, compatible with recent dax refactoring. Testing ------- The famfs user space [5] includes comprehensive smoke and unit tests that exercise all three components together. The ndctl series includes a dedicated test for famfs mode transitions. References ---------- [1] https://lore.kernel.org/linux-cxl/cover.1708709155.git.john@groves.net/ [2] https://lore.kernel.org/linux-cxl/cover.1714409084.git.john@groves.net/ [3] https://lwn.net/Articles/983105/ (LSFMM 2024) [4] https://lwn.net/Articles/1020170/ (LSFMM 2025) [5] https://famfs.org (famfs user space) [6] https://lore.kernel.org/linux-cxl/20250703185032.46568-1-john@groves.net/ (V2) -- John Groves