On Wed, May 20, 2020 at 9:24 AM Amir Goldstein <amir73il@xxxxxxxxx> wrote: > > On Wed, May 20, 2020 at 4:02 AM cgxu <cgxu519@xxxxxxxxxxxx> wrote: > > > > On 5/6/20 5:53 PM, Chengguang Xu wrote: > > > 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 patch tries to only sync target dirty upper inodes which are belong > > > to specific overlayfs instance and wait for completion. By doing this, > > > it is able to reduce cost of synchronization and will not seriously impact > > > IO performance of unrelated processes. > > > > > > Signed-off-by: Chengguang Xu <cgxu519@xxxxxxxxxxxx> > > > > Except explicit sycnfs is triggered by user process, there is also implicit > > syncfs during umount process of overlayfs instance. Every syncfs will > > deliver to upper fs and whole dirty data of upper fs syncs to persistent > > device at same time. > > > > In high density container environment, especially for temporary jobs, > > this is quite unwilling behavior. Should we provide an option to > > mitigate this effect for containers which don't care about dirty data? If containers don't care about dirty data, why go to great lengths to make sure that syncfs() works? Can't we just have an option to turn off syncing completely, for fsync, for syncfs, for shutdown, for everything? That would be orders of magnitude simpler than the patch you posted. Thanks, Miklos
