On Thu, Aug 03, 2023 at 04:34:48PM +1000, Dave Chinner wrote: > On Wed, Aug 02, 2023 at 10:22:18PM -0700, Darrick J. Wong wrote: > > From: Darrick J. Wong <djwong@xxxxxxxxxx> > > > > If the fscounters scrubber notices incorrect summary counters, it's > > entirely possible that scrub is simply racing with other threads that > > are updating the incore counters. There isn't a good way to stabilize > > percpu counters or set ourselves up to observe live updates with hooks > > like we do for the quotacheck or nlinks scanners, so we instead choose > > to freeze the filesystem long enough to walk the incore per-AG > > structures. > > > > Past me thought that it was going to be commonplace to have to freeze > > the filesystem to perform some kind of repair and set up a whole > > separate infrastructure to freeze the filesystem in such a way that > > userspace could not unfreeze while we were running. This involved > > adding a mutex and freeze_super/thaw_super functions and dealing with > > the fact that the VFS freeze/thaw functions can free the VFS superblock > > references on return. > > > > This was all very overwrought, since fscounters turned out to be the > > only user of scrub freezes, and it doesn't require the log to quiesce, > > only the incore superblock counters. We prevent other threads from > > changing the freeze level by calling freeze_super_excl with a custom > > freeze cookie to keep everyone else out of the filesystem. > > > > The end result is that fscounters should be much more efficient. When > > we're checking a busy system and we can't stabilize the counters, the > > custom freeze will do less work, which should result in less downtime. > > Repair should be similarly speedy, but that's in the next patch. > > > > Signed-off-by: Darrick J. Wong <djwong@xxxxxxxxxx> > > --- > > fs/xfs/scrub/fscounters.c | 198 ++++++++++++++++++++++++++++++++++----------- > > fs/xfs/scrub/fscounters.h | 20 +++++ > > fs/xfs/scrub/scrub.c | 6 + > > fs/xfs/scrub/scrub.h | 1 > > fs/xfs/scrub/trace.h | 26 ++++++ > > 5 files changed, 203 insertions(+), 48 deletions(-) > > create mode 100644 fs/xfs/scrub/fscounters.h > > Code changes look ok, though I am wondering why struct > xchk_fscounters needs to be moved to it's own header file? AFAICT it > is still only used by fs/xfs/scrub/fscounters.c, so I'm not sure > what purpose the new header file serves.... The header file is the basis for the repair patch which I've previously sent to the list. https://lore.kernel.org/linux-xfs/168506061531.3732954.7713322896089390150.stgit@frogsfrogsfrogs/ It's not strictly needed at this time. I'll resend without that bit. --D > -Dave. > -- > Dave Chinner > david@xxxxxxxxxxxxx
