Hello everyone, I've pushed out my work to optimize file and directory fsyncs (as well as O_SYNC writes). It includes a new disk format. I'll post some benchmarks next week, but in general this should be much more usable in mail server workloads. Details on how it all works can be found in tree-log.c comments. The short version is that instead of an fsync doing a full FS commit, items for a given file or directory that have been changed by the current transaction are copied into a log tree. This log tree uses the same copy on write code as all the other trees in the FS, but the super block has pointers to a tree of log tree roots, and synchronous FS ops are changed to write an updated super block with just the pointer to the log trees modified. After a crash, items and extent pointers are copied out of the log tree back into the main FS. The end result is that fsyncs don't commit the extent tree or force a recow of any subvolume tree blocks, which is what made them so expensive in the old code. fsyncs in one subvolume don't force other subvolumes to flush all of their blocks to disk. fsyncs in one file don't force any other files or directories down to disk. In other words, it makes the impact of an fsync much smaller in every workload. Blocks for the log tree come out of the metadata block groups. So they have the same raid levels and duplication rules as the rest of the metadata. -chris -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
