Current syncfs(2) syscall on overlayfs just calls sync_filesystem() on upper_sb to synchronize whole dirty inodes in upper filesystem regardless of the overlay ownership of the inode. In the use case of container, when multiple containers using the same underlying upper filesystem, it has some shortcomings as below. (1) Performance Synchronization is probably heavy because it actually syncs unnecessary inodes for target overlayfs. (2) Interference Unplanned synchronization will probably impact IO performance of unrelated container processes on the other overlayfs. This series try to implement containerized syncfs for overlayfs so that only sync target dirty upper inodes which are belong to specific overlayfs instance. By doing this, it is able to reduce cost of synchronization and will not seriously impact IO performance of unrelated processes. v1->v2: - Mark overlayfs' inode dirty itself instead of adding notification mechanism to vfs inode. v2->v3: - Introduce overlayfs' extra syncfs wait list to wait target upper inodes in ->sync_fs. v3->v4: - Using wait_sb_inodes() to wait syncing upper inodes. - Mark overlay inode dirty only when having upper inode and VM_SHARED flag in ovl_mmap(). - Check upper i_state after checking upper mmap state in ovl_write_inode. v4->v5: - Add underlying inode dirtiness check after mnt_drop_write(). - Handle both wait/no-wait mode of syncfs(2) in overlayfs' ->sync_fs(). Chengguang Xu (10): ovl: setup overlayfs' private bdi ovl: implement ->writepages operation ovl: implement overlayfs' ->evict_inode operation ovl: mark overlayfs' inode dirty on modification ovl: mark overlayfs' inode dirty on shared mmap ovl: implement overlayfs' ->write_inode operation ovl: cache dirty overlayfs' inode fs: export wait_sb_inodes() fs: introduce new helper sync_fs_and_blockdev() ovl: implement containerized syncfs for overlayfs fs/fs-writeback.c | 3 +- fs/overlayfs/file.c | 6 ++++ fs/overlayfs/inode.c | 14 ++++++++ fs/overlayfs/overlayfs.h | 4 +++ fs/overlayfs/super.c | 69 ++++++++++++++++++++++++++++++++++----- fs/overlayfs/util.c | 21 ++++++++++++ fs/sync.c | 14 +++++--- include/linux/fs.h | 1 + include/linux/writeback.h | 1 + 9 files changed, 120 insertions(+), 13 deletions(-) -- 2.27.0
