On Thu, Nov 25, 2021 at 03:05:23PM +0800, Jeffle Xu wrote: > changes since v7: > - rebase to v5.16 > - patch 2: rename FUSE_DAX_NONE|FUSE_DAX_INODE to > FUSE_DAX_INODE_DEFAULT|FUSE_DAX_INODE_USER > - patch 5: remove redundant call for fuse_is_inode_dax_mode() in > process_init_reply() > - patch 5: if server's map alignment is non-compliant (fail > fuse_dax_check_alignment()), the mounted fs won't work and users are > required to remount it explicitly, instead of silently falling back to > 'never' mode. Thanks Jeffle for this work. These patches look good to me. I have done a basic testing with it and it seems to work as expected. Hence I have provided my Reviewed-by tags for all the patches. Now it is up to the Miklos to decide whether he likes the patches or not. Thanks Vivek > > Corresponding changes to virtiofsd: > https://www.mail-archive.com/virtio-fs@xxxxxxxxxx/msg04349.html > > v7: https://lore.kernel.org/all/c41837f0-a183-d911-885d-cf3bcdd9b7c8@xxxxxxxxxxxxxxxxx/T/ > v6: https://lore.kernel.org/all/20211011030052.98923-1-jefflexu@xxxxxxxxxxxxxxxxx/ > v5: https://lore.kernel.org/all/20210923092526.72341-1-jefflexu@xxxxxxxxxxxxxxxxx/ > v4: https://lore.kernel.org/linux-fsdevel/20210817022220.17574-1-jefflexu@xxxxxxxxxxxxxxxxx/ > v3: https://www.spinics.net/lists/linux-fsdevel/msg200852.html > v2: https://www.spinics.net/lists/linux-fsdevel/msg199584.html > v1: https://www.spinics.net/lists/linux-virtualization/msg51008.html > > Original Rationale for this Patchset > ==================================== > > This patchset adds support of per-file DAX for virtiofs, which is > inspired by Ira Weiny's work on ext4[1] and xfs[2]. > > Any comment is welcome. > > [1] commit 9cb20f94afcd ("fs/ext4: Make DAX mount option a tri-state") > [2] commit 02beb2686ff9 ("fs/xfs: Make DAX mount option a tri-state") > > [Purpose] > DAX may be limited in some specific situation. When the number of usable > DAX windows is under watermark, the recalim routine will be triggered to > reclaim some DAX windows. It may have a negative impact on the > performance, since some processes may need to wait for DAX windows to be > recalimed and reused then. To mitigate the performance degradation, the > overall DAX window need to be expanded larger. > > However, simply expanding the DAX window may not be a good deal in some > scenario. To maintain one DAX window chunk (i.e., 2MB in size), 32KB > (512 * 64 bytes) memory footprint will be consumed for page descriptors > inside guest, which is greater than the memory footprint if it uses > guest page cache when DAX disabled. Thus it'd better disable DAX for > those files smaller than 32KB, to reduce the demand for DAX window and > thus avoid the unworthy memory overhead. > > Per-file DAX feature is introduced to address this issue, by offering a > finer grained control for dax to users, trying to achieve a balance > between performance and memory overhead. > > > [Note] > When the per-file DAX hint changes while the file is still *opened*, it > is quite complicated and maybe fragile to dynamically change the DAX > state, since dynamic switching needs to switch a_ops atomiclly. Ira > Weiny had ever implemented a so called i_aops_sem lock [3] but > eventually gave up since the complexity of the implementation > [4][5][6][7]. > > Hence mark the inode and corresponding dentries as DONE_CACHE once the > per-file DAX hint changes, so that the inode instance will be evicted > and freed as soon as possible once the file is closed and the last > reference to the inode is put. And then when the file gets reopened next > time, the new instantiated inode will reflect the new DAX state. > > In summary, when the per-file DAX hint changes for an *opened* file, the > DAX state of the file won't be updated until this file is closed and > reopened later. This is also how ext4/xfs per-file DAX works. > > [3] https://lore.kernel.org/lkml/20200227052442.22524-7-ira.weiny@xxxxxxxxx/ > [4] https://patchwork.kernel.org/project/xfs/cover/20200407182958.568475-1-ira.weiny@xxxxxxxxx/ > [5] https://lore.kernel.org/lkml/20200305155144.GA5598@xxxxxx/ > [6] https://lore.kernel.org/lkml/20200401040021.GC56958@magnolia/ > [7] https://lore.kernel.org/lkml/20200403182904.GP80283@magnolia/ > > > Jeffle Xu (7): > fuse: add fuse_should_enable_dax() helper > fuse: make DAX mount option a tri-state > fuse: support per inode DAX in fuse protocol > fuse: enable per inode DAX > fuse: negotiate per inode DAX in FUSE_INIT > fuse: mark inode DONT_CACHE when per inode DAX hint changes > Documentation/filesystem/dax: DAX on virtiofs > > Documentation/filesystems/dax.rst | 20 +++++++++++++++-- > fs/fuse/dax.c | 36 +++++++++++++++++++++++++++++-- > fs/fuse/file.c | 4 ++-- > fs/fuse/fuse_i.h | 28 ++++++++++++++++++++---- > fs/fuse/inode.c | 28 +++++++++++++++++------- > fs/fuse/virtio_fs.c | 18 +++++++++++++--- > include/uapi/linux/fuse.h | 5 +++++ > 7 files changed, 118 insertions(+), 21 deletions(-) > > -- > 2.27.0 >
