On Thu, Feb 27, 2020 at 08:43:12AM -0500, Brian Foster wrote: > Hi all, > > Here's a v5 RFC of the automatic item relogging experiment. Firstly, > note that this is still a POC and experimental code with various quirks. Heh, funny, I was going to ask you if you might have time next week to review the latest iteration of the btree bulk loading series so that I could get closer to merging the rest of online repair and/or refactoring offline repair. I'll take a closer look at this after I read through everything else that came in overnight. --D > Some are documented in the code, others might not be (such as abusing > the AIL lock, etc.). The primary purpose of this series is still to > express and review a fundamental design. Based on discussion on the last > version, there is specific focus towards addressing log reservation and > pre-item locking deadlock vectors. While the code is still quite hacky, > I believe this design addresses both of those fundamental issues. > Further details on the design and approach are documented in the > individual commit logs. > > In addition, the final few patches introduce buffer relogging capability > and test infrastructure, which currently has no use case other than to > demonstrate development flexibility and the ability to support arbitrary > log items in the future, if ever desired. If this approach is taken > forward, the current use cases are still centered around intent items > such as the quotaoff use case and extent freeing use case defined by > online repair of free space trees. > > On somewhat of a tangent, another intent oriented use case idea crossed > my mind recently related to the long standing writeback stale data > exposure problem (i.e. if we crash after a delalloc extent is converted > but before writeback fully completes on the extent). The obvious > approach of using unwritten extents has been rebuffed due to performance > concerns over extent conversion. I wonder if we had the ability to log a > "writeback pending" intent on some reasonable level of granularity (i.e. > something between a block and extent), whether we could use that to > allow log recovery to zero (or convert) such extents in the event of a > crash. This is a whole separate design discussion, however, as it > involves tracking outstanding writeback, etc. In this context it simply > serves as a prospective use case for relogging, as such intents would > otherwise risk similar log subsystem deadlocks as the quotaoff use case. > > Thoughts, reviews, flames appreciated. > > Brian > > rfcv5: > - More fleshed out design to prevent log reservation deadlock and > locking problems. > - Split out core patches between pre-reservation management, relog item > state management and relog mechanism. > - Added experimental buffer relogging capability. > rfcv4: https://lore.kernel.org/linux-xfs/20191205175037.52529-1-bfoster@xxxxxxxxxx/ > - AIL based approach. > rfcv3: https://lore.kernel.org/linux-xfs/20191125185523.47556-1-bfoster@xxxxxxxxxx/ > - CIL based approach. > rfcv2: https://lore.kernel.org/linux-xfs/20191122181927.32870-1-bfoster@xxxxxxxxxx/ > - Different approach based on workqueue and transaction rolling. > rfc: https://lore.kernel.org/linux-xfs/20191024172850.7698-1-bfoster@xxxxxxxxxx/ > > Brian Foster (9): > xfs: set t_task at wait time instead of alloc time > xfs: introduce ->tr_relog transaction > xfs: automatic relogging reservation management > xfs: automatic relogging item management > xfs: automatic log item relog mechanism > xfs: automatically relog the quotaoff start intent > xfs: buffer relogging support prototype > xfs: create an error tag for random relog reservation > xfs: relog random buffers based on errortag > > fs/xfs/libxfs/xfs_errortag.h | 4 +- > fs/xfs/libxfs/xfs_shared.h | 1 + > fs/xfs/libxfs/xfs_trans_resv.c | 24 +++- > fs/xfs/libxfs/xfs_trans_resv.h | 1 + > fs/xfs/xfs_buf_item.c | 5 + > fs/xfs/xfs_dquot_item.c | 7 ++ > fs/xfs/xfs_error.c | 3 + > fs/xfs/xfs_log.c | 2 +- > fs/xfs/xfs_qm_syscalls.c | 12 +- > fs/xfs/xfs_trace.h | 3 + > fs/xfs/xfs_trans.c | 79 +++++++++++- > fs/xfs/xfs_trans.h | 13 +- > fs/xfs/xfs_trans_ail.c | 216 ++++++++++++++++++++++++++++++++- > fs/xfs/xfs_trans_buf.c | 35 ++++++ > fs/xfs/xfs_trans_priv.h | 6 + > 15 files changed, 399 insertions(+), 12 deletions(-) > > -- > 2.21.1 >
