On Mon, Jun 21, 2021 at 04:22:35PM +0200, Christoph Hellwig wrote: > On Mon, Jun 21, 2021 at 03:16:50PM +0100, Matthew Wilcox wrote: > > On Mon, Jun 21, 2021 at 04:09:56PM +0200, Christoph Hellwig wrote: > > > On Mon, Jun 21, 2021 at 03:03:07PM +0100, Matthew Wilcox wrote: > > > > i suggested that to viro last night, and he pointed out that ioctl(S_SYNC) > > > > > > Where would that S_SYNC ioctl be implemented? > > > > xfs_diflags_to_iflags( > > if (xflags & FS_XFLAG_SYNC) > > flags |= S_SYNC; > > > > (mutatis mutandi per filesystem) > > > Ok, your description above wasn't very exact. Sorry - the relevant part of conversation went < viro> willy: that's the part that can't be done at open() time < willy> because we might mount -o remount,sync after open()? < viro> ... as well as setting S_SYNC via ioctl Should've been phrased better... > Anyway, that at least doesn't go out to the superblock. But if Al > dislikes it we can also make generic_sync_file and friends check > IS_SYNC() again. Having a single flag is kinda nice as it avoids > stupid errors, but if we actually have a performance problem here > (do we have any data on that?) just going back to the old way would > seem like the simplest fix. IIRC, there had been profiling data posted with init_sync_kiocb() responsible for large part of new_sync_write()/new_sync_read() overhead. Remember the threads about the use of ->read_iter()/->write_iter() being slower than having ->read()/->write()? Back in December or so, I think; one surprising part had been that large chunk of overhead sat not in suboptimal iov_iter primitives, but right in new_sync_read()/new_sync_write() with init_sync_kiocb() being the source of it, I'd rather have a single helper for those checks, rather than open-coding IS_SYNC() + IOCB_DSYNC in each, for obvious reasons...
