Re: [PATCH BUNDLE v7] famfs: Fabric-Attached Memory File System

Alireza Sanaee
2026-01-20T09:12:27Z

On Sun, 18 Jan 2026 22:29:18 +0000
John Groves <john@jagalactic.com> wrote:

Hi John,

I wonder if these new patches sent recently have been reflected on the github repo readme files. It seems it is not, is it?

> This is a coordinated patch submission for famfs (Fabric-Attached Memory
> File System) across three repositories:
>
> 1. Linux kernel (cover + 19 patches) - dax fsdev driver + fuse/famfs
> integration
> 2. libfuse (cover + 3 patches) - famfs protocol support for fuse servers
> 3. ndctl/daxctl (cover + 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 (V7, 19 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 (V7, 3 patches):
> - Updates fuse_kernel.h to kernel 6.19 baseline
> - Adds famfs DAX fmap protocol definitions
> - Implements famfs DAX fmap support for fuse servers
>
> ndctl/daxctl (V4, 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)
> [7] https://lore.kernel.org/linux-fsdevel/20260107153244.64703-1-john@groves.net/T/#m0000d8c00290f48c086b8b176c7525e410f8508c (related ndctl series)
> --
> John Groves
>
>
>