Hi all, This patch series introduces a totally new filesystem summary counter online scrub feature. Whereas previous iterations froze the filesystem to count inodes and free blocks, this one drastically reduces overhead by loosening its precision somewhat. Instead of freezing the fs, we "locklessly" compute the expected summary counter values using incore per-AG counters. Once the expected value is computed, we employ thresholding to check that the counter values are in the right ballpark but aren't necessarily exactly correct. The first patch implements a per-cpu counter of the number of blocks being held in delayed allocation reservations. This should represent the difference between the incore fdblocks counter and the one that would be recorded on disk if one were to iterate all the committed metadata structures. Patch #2 renames some confusingly named functions in xfs_icache.c so that the file no longer uses "reclaim" when referring to memory reclamation and garbage collecting of speculative preallocations. Patch #3 enables the scrub code to pause the posteof and cowblocks background reclamation workers temporarily to reduce perturbations in the summary counters while the scrubber runs. This isn't totally foolproof since they can be re-armed, but we only need ballpark correctness. Patch #4 teaches the AGF and AGI header scrub functions to check the incore per-AG counters against the on-disk headers. Finally, patch #5 implements the actual fs summary counter scrubber 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. --D kernel git tree: https://git.kernel.org/cgit/linux/kernel/git/djwong/xfs-linux.git/log/?h=scrub-summary-counters xfsprogs git tree: https://git.kernel.org/cgit/linux/kernel/git/djwong/xfsprogs-dev.git/log/?h=scrub-summary-counters
