From: Ira Weiny <ira.weiny@xxxxxxxxx> Changes from V7: Add DCACHE_DONTCACHE If mount override don't worry about inode caching Change mount flags to NEVER/ALWAYS Clean up xfs_inode_enable_dax() Clarify comments Update documentation At LSF/MM'19 [1] [2] we discussed applications that overestimate memory consumption due to their inability to detect whether the kernel will instantiate page cache for a file, and cases where a global dax enable via a mount option is too coarse. The following patch series enables the use of DAX on individual files and/or directories on xfs, and lays some groundwork to do so in ext4. It further enhances the dax mount option to be a tri-state of 'always', 'never', or 'iflag' (default). Furthermore, it maintians '-o dax' to be equivalent to '-o dax=always'. The insight at LSF/MM was to separate the per-mount or per-file "physical" (FS_XFLAG_DAX) capability switch from an "effective" (S_DAX) attribute for the file. At LSF/MM we discussed the difficulties of switching the DAX state of a file with active mappings / page cache. It was thought the races could be avoided by limiting DAX state flips to 0-length files. However, this turns out to not be true.[3][5] This is because address space operations (a_ops) may be in use at any time the inode is referenced. For this reason direct manipulation of the FS_XFLAG_DAX is allowed but the operation of the file (S_DAX) is not immediately changed. Details of when and how DAX state can be changed on a file is included in a documentation patch. It should be noted that FS_XFLAG_DAX inheritance is not shown in this patch set as it was maintained from previous work on XFS. FS_XFLAG_DAX and it's inheritance will need to be added to other file systems for user control. [1] https://lwn.net/Articles/787973/ [2] https://lwn.net/Articles/787233/ [3] https://lkml.org/lkml/2019/10/20/96 [4] https://patchwork.kernel.org/patch/11310511/ [5] https://lore.kernel.org/lkml/20200405061945.GA94792@xxxxxxxxxxxxxxxxxxxxxxxxx/ To: linux-kernel@xxxxxxxxxxxxxxx Cc: "Darrick J. Wong" <darrick.wong@xxxxxxxxxx> Cc: Dan Williams <dan.j.williams@xxxxxxxxx> Cc: Dave Chinner <david@xxxxxxxxxxxxx> Cc: Christoph Hellwig <hch@xxxxxx> Cc: "Theodore Y. Ts'o" <tytso@xxxxxxx> Cc: Jan Kara <jack@xxxxxxx> Cc: linux-ext4@xxxxxxxxxxxxxxx Cc: linux-xfs@xxxxxxxxxxxxxxx Cc: linux-fsdevel@xxxxxxxxxxxxxxx Changes from V6: Incorporate feedback on patches Add ability to change FS_XFLAG_DAX on files at any time. Add a don't cache flag to the VFS layer Preserve internal XFS IDONTCACHE behavior for bulkstat operations Changes from V5: * make dax mount option a tri-state * Reject changes to FS_XFLAG_DAX for regular files - Allow only on directories * Update documentation Changes from V4: * Open code the aops lock rather than add it to the xfs_ilock() subsystem (Darrick's comments were obsoleted by this change) * Fix lkp build suggestions and bugs Changes from V3: * Remove global locking... :-D * put back per inode locking and remove pre-mature optimizations * Fix issues with Directories having IS_DAX() set * Fix kernel crash issues reported by Jeff * Add some clean up patches * Consolidate diflags to iflags functions * Update/add documentation * Reorder/rename patches quite a bit Changes from V2: * Move i_dax_sem to be a global percpu_rw_sem rather than per inode Internal discussions with Dan determined this would be easier, just as performant, and slightly less overhead that having it in the SB as suggested by Jan * Fix locking order in comments and throughout code * Change "mode" to "state" throughout commits * Add CONFIG_FS_DAX wrapper to disable inode_[un]lock_state() when not configured * Add static branch for which is activated by a device which supports DAX in XFS * Change "lock/unlock" to up/down read/write as appropriate Previous names were over simplified * Update comments/documentation * Remove the xfs specific lock to the vfs (global) layer. * Fix i_dax_sem locking order and comments * Move 'i_mapped' count from struct inode to struct address_space and rename it to mmap_count * Add inode_has_mappings() call * Fix build issues * Clean up syntax spacing and minor issues * Update man page text for STATX_ATTR_DAX * Add reviewed-by's * Rebase to 5.6 Rename patch: from: fs/xfs: Add lock/unlock state to xfs to: fs/xfs: Add write DAX lock to xfs layer Add patch: fs/xfs: Clarify lockdep dependency for xfs_isilocked() Drop patch: fs/xfs: Fix truncate up Ira Weiny (11): fs/xfs: Remove unnecessary initialization of i_rwsem fs: Remove unneeded IS_DAX() check in io_is_direct() fs/stat: Define DAX statx attribute fs/xfs: Change XFS_MOUNT_DAX to XFS_MOUNT_DAX_ALWAYS fs/xfs: Make DAX mount option a tri-state fs/xfs: Create function xfs_inode_enable_dax() fs/xfs: Combine xfs_diflags_to_linux() and xfs_diflags_to_iflags() fs: Define I_DONTCACNE in VFS layer fs: Introduce DCACHE_DONTCACHE fs/xfs: Change xfs_ioctl_setattr_dax_invalidate() Documentation/dax: Update Usage section Documentation/filesystems/dax.txt | 166 +++++++++++++++++++++++++++++- drivers/block/loop.c | 6 +- fs/dcache.c | 4 + fs/inode.c | 15 +++ fs/stat.c | 3 + fs/xfs/xfs_icache.c | 4 +- fs/xfs/xfs_inode.h | 1 + fs/xfs/xfs_ioctl.c | 138 ++++--------------------- fs/xfs/xfs_iops.c | 72 ++++++++----- fs/xfs/xfs_mount.h | 3 +- fs/xfs/xfs_super.c | 46 ++++++++- include/linux/dcache.h | 2 + include/linux/fs.h | 14 +-- include/uapi/linux/stat.h | 1 + 14 files changed, 312 insertions(+), 163 deletions(-) -- 2.25.1
