On Thu, Mar 05, 2020 at 04:51:44PM +0100, Christoph Hellwig wrote: > FYI, I still will fully NAK any series that adds additional locks > and thus atomic instructions to basically every fs call, and grows > the inode by a rw_semaphore plus and atomic64_t. I also think the > whole idea of switching operation vectors at runtime is fatally flawed > and we should never add such code, nevermind just for a fringe usecase > of a fringe feature. Being new to this area of the kernel I'm not clear on the history... It was my understanding that the per-file flag support was a requirement to removing the experimental designation from DAX. Is this still the case? Ira > > On Wed, Feb 26, 2020 at 09:24:30PM -0800, ira.weiny@xxxxxxxxx wrote: > > From: Ira Weiny <ira.weiny@xxxxxxxxx> > > > > 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 > > > > > > 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 selecting the use of DAX on individual files > > and/or directories on xfs, and lays some groundwork to do so in ext4. In this > > scheme the dax mount option can be omitted to allow the per-file property to > > take effect. > > > > The insight at LSF/MM was to separate the per-mount or per-file "physical" > > capability switch from an "effective" 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] This is because address space > > operations (a_ops) may be in use at any time the inode is referenced and users > > have expressed a desire to be able to change the DAX state on a file with data > > in it. For those reasons this patch set allows changing the DAX state flag on > > a file as long as it is not current mapped. > > > > Details of when and how DAX state can be changed on a file is included in a > > documentation patch. > > > > It should be noted that the physical DAX flag inheritance is not shown in this > > patch set as it was maintained from previous work on XFS. The physical DAX > > flag and it's inheritance will need to be added to other file systems for user > > control. > > > > As submitted this works on real hardware testing. > > > > > > [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/ > > > > > > To: linux-kernel@xxxxxxxxxxxxxxx > > Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx> > > 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 > > > > > > Ira Weiny (12): > > fs/xfs: Remove unnecessary initialization of i_rwsem > > fs: Remove unneeded IS_DAX() check > > fs/stat: Define DAX statx attribute > > fs/xfs: Isolate the physical DAX flag from enabled > > fs/xfs: Create function xfs_inode_enable_dax() > > fs: Add locking for a dynamic address space operations state > > fs: Prevent DAX state change if file is mmap'ed > > fs/xfs: Hold off aops users while changing DAX state > > fs/xfs: Clean up locking in dax invalidate > > fs/xfs: Allow toggle of effective DAX flag > > fs/xfs: Remove xfs_diflags_to_linux() > > Documentation/dax: Update Usage section > > > > Documentation/filesystems/dax.txt | 84 +++++++++++++++++++++++++- > > Documentation/filesystems/vfs.rst | 16 +++++ > > fs/attr.c | 1 + > > fs/inode.c | 16 ++++- > > fs/iomap/buffered-io.c | 1 + > > fs/open.c | 4 ++ > > fs/stat.c | 5 ++ > > fs/xfs/xfs_icache.c | 5 +- > > fs/xfs/xfs_inode.h | 2 + > > fs/xfs/xfs_ioctl.c | 98 +++++++++++++++---------------- > > fs/xfs/xfs_iops.c | 69 +++++++++++++++------- > > include/linux/fs.h | 73 ++++++++++++++++++++++- > > include/uapi/linux/stat.h | 1 + > > mm/fadvise.c | 7 ++- > > mm/filemap.c | 4 ++ > > mm/huge_memory.c | 1 + > > mm/khugepaged.c | 2 + > > mm/mmap.c | 19 +++++- > > mm/util.c | 9 ++- > > 19 files changed, 328 insertions(+), 89 deletions(-) > > > > -- > > 2.21.0 > ---end quoted text---
