On Mon, 2009-11-23 at 11:44 -0500, J. Bruce Fields wrote: > If the side we want to optimize is the modifications, I wonder if we > could do all the i_version increments on *read* of i_version?: > > - writes (and other inode modifications) set an "i_version_dirty" > flag. > - reads of i_version clear the i_version_dirty flag, increment > i_version, and return the result. > > As long as the reader sees i_version_flag set only after it sees the > write that caused it, I think it all works? That probably won't make much of a difference to performance. Most NFSv4 clients will have every WRITE followed by a GETATTR operation in the same compound, so your i_version_dirty flag will always immediately get cleared. The question is, though, why does the jbd2 machinery need to be engaged on _every_ write? The NFS clients don't care if we lose an i_version count due to a sudden server reboot, since that will trigger a rewrite of the dirty data anyway once the server comes back up again. As long as the i_version is guaranteed to be written to stable storage on a successful call to fsync(), then the NFS data integrity requirements are fully satisfied. Trond -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
