On Thu, Jul 27, 2023 at 03:18:32PM -0700, Darrick J. Wong wrote: > Hi all, > > These patches fix a few problems that I noticed in the code that deals > with old btree blocks after a successful repair. > > First, I observed that it is possible for repair to incorrectly > invalidate and delete old btree blocks if they were crosslinked. The > solution here is to consult the reverse mappings for each block in the > extent -- singly owned blocks are invalidated and freed, whereas for > crosslinked blocks, we merely drop the incorrect reverse mapping. > > A largeish change in this patchset is moving the reaping code to a > separate file, because the code are mostly interrelated static > functions. For now this also drops the ability to reap file blocks, > which will return when we add the bmbt repair functions. > > Second, we convert the reap function to use EFIs so that we can commit > to freeing as many blocks in as few transactions as we dare. We would > like to free as many old blocks as we can in the same transaction that > commits the new structure to the ondisk filesystem to minimize the > number of blocks that leak if the system crashes before the repair fully > completes. > > The third change made in this series is to avoid tripping buffer cache > assertions if we're merely scanning the buffer cache for buffers to > invalidate, and find a non-stale buffer of the wrong length. This is > primarily cosmetic, but makes my life easier. > > The fourth change restructures the reaping code to try to process as many > blocks in one go as possible, to reduce logging traffic. > > The last change switches the reaping mechanism to use per-AG bitmaps > defined in a previous patchset. This should reduce type confusion when > reading the source code. > > If you're going to start using this mess, you probably ought to just > pull from my git trees, which are linked below. > > This is an extraordinary way to destroy everything. Enjoy! > Comments and questions are, as always, welcome. Overall I don't see any red flags, so from that perspective I think it's good to merge as is. THe buffer cache interactions are much neater this time around. Reviewed-by: Dave Chinner <dchinner@xxxxxxxxxx> The main thing I noticed is that the deferred freeing mechanism ifo rbulk reaping will add up to 128 XEFIs to the transaction. That could result in a single EFI with up to 128 extents in it, right? What happens when we try to free that many extents in a single transaction loop? The extent free processing doesn't have a "have we run out of transaction reservation" check in it like the refcount item processing does, so I don't think it can roll to renew the transaction reservation if it is needed. DO we need to catch this and renew the reservation by returning -EAGAIN from xfs_extent_free_finish_item() if there isn't enough of a reservation remaining to free an extent? -Dave. -- Dave Chinner david@xxxxxxxxxxxxx
