On Mon, Jan 15, 2018 at 8:33 AM, Chengguang Xu <cgxu519@xxxxxxxxxx> wrote: > Currently syncfs(2) call on overlayfs just simply call 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 > irrelative container processes on the other overlayfs. > > This patch iterates upper inode list in overlayfs to only sync target > dirty inodes and wait for completion. By doing this, It is able to reduce > cost of synchronization and will not seriously impact IO performance of > irrelative processes. In special case, when having very few dirty inodes > and a lot of clean upper inodes in overlayfs, then iteration may waste > time so that synchronization is slower than before, but we think the > potential for performance improvement far surpass the potential for > performance regression in most cases. > > Signed-off-by: Chengguang Xu <cgxu519@xxxxxxxxxx> > --- > Changes since v3: > - Introduce upper_inode list to organize ovl indoe which has upper inode. Where is the inode removed from the list? Should be done in ovl_destroy_inode(). Problem is: we can drop the overlay inode even when the underlying inode is dirty, so we need to sync the upper inode before letting it go in ovl_destroy_inode(). Thanks, Miklos -- To unsubscribe from this list: send the line "unsubscribe linux-unionfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
