On Wed, Feb 19, 2025 at 06:35:27AM +0100, Christoph Hellwig wrote: > On Tue, Feb 18, 2025 at 12:23:27PM -0800, Darrick J. Wong wrote: > > On Mon, Feb 17, 2025 at 10:31:28AM +0100, Christoph Hellwig wrote: > > > The buffer cache keeps a bt_io_count per-CPU counter to track all > > > in-flight I/O, which is used to ensure no I/O is in flight when > > > unmounting the file system. > > > > > > For most I/O we already keep track of inflight I/O at higher levels: > > > > > > - for synchronous I/O (xfs_buf_read/xfs_bwrite/xfs_buf_delwri_submit), > > > the caller has a reference and waits for I/O completions using > > > xfs_buf_iowait > > > - for xfs_buf_delwri_submit the only caller (AIL writeback) tracks the > > > > Do you mean xfs_buf_delwri_submit_nowait here? > > Yes. > > > IOWs, only asynchronous readahead needs an explicit counter in the > > xfs_buf to prevent unmount because: > > > > 0. Anything done in mount/unmount/freeze holds s_umount > > 1. Buffer reads done on behalf of a file hold the file open and pin the > > mount > > 2. Dirty buffers have log items, and we can't unmount until those are > > dealt with > > 3. Fsck holds an open fd and hence pins the mount > > 4. Unmount blocks until background gc finishes > > > > Right? > > Yes. > > > I almost wonder if you could just have a percpu counter in the > > xfs_mount but that sounds pretty hot. > > Well, that would remove the nice xfs_buftarg_wait() abstraction. > Givne that we don't even allocate an extra buftrag unless we use > it that doesn't seem very useful. Heheh. Anyway, the changes look good to me so with that cleared up Reviewed-by: "Darrick J. Wong" <djwong@xxxxxxxxxx> > > > + /* there are currently no valid flags for xfs_buf_get_uncached */ > > > + ASSERT(flags == 0); > > > > Can we just get rid of flags then? AFAICT nobody uses it either here or > > in xfsprogs, and in fact I think there's a nasty bug in the userspace > > rtsb code: > > See my reply to the last patch: I actually have a patch to remove it, > but it conflicts with the zoned series. So for now I'll defer it until > that is merged. <nod> --D
