On Fri, Jul 22, 2011 at 11:47:32PM +0200, Andi Kleen wrote: > On Fri, Jul 22, 2011 at 04:11:42PM -0500, Matt Mackall wrote: > > On Fri, 2011-07-22 at 22:59 +0200, Andi Kleen wrote: > > > > Indeed. Only usefully exists on ext4 and requires extra system calls. > > > > > > Not sure what you mean? It's in stat(2), just like the timestamps. > > > > I don't see anything that looks like a version or generation number in > > either the man pages, the asm-generic/stat.h, or glibc's asm/stat.h. > > Pointer? > > Hmm you're right. I thought it was in there, but apparently not. > I think it should be added there though. We still have some unused > fields. But last I checked I thought it was only ext4 that actually incremented the i_version on IO, and even then only when given a (non-default) mount option. My notes on what needs to be done there: - collect data to determine whether turning on i_version causes any significant performance regressions. - Last I talked to him, Ted Tso recommended running Bonnie on a local disk, since it does a lot of little writes, which is somewhat of a worst case, as it will generate extra metadata updates for each write. Compare total wall-clock time, number of iops, and number of bytes (using some kind of block tracing). - If there aren't any problems, turn it on by default, and we're done. If there are unfixable problems, consider something more complicated (like turning on i_version automatically when someone asks for it). - We need to check that i_version is also doing something sensible on directory as well as on file inodes. - We also need to think about what it does after reboots. (E.g. what is an nfs server to do if clients see the i_version go backwards (and hence possible repeat old values) after a reboot?) - Double-check the order that data updates and i_version updates are done in. (Ideal would be if they were atomic, but for nfsd's purposes at least it should be adequate if the i_version comes after, and no later than the next commit.) --b. -- 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
