Hey Eric, Can you or Ric put in a good word with Ulrich (through appropriate Red Hat channels, if that would be helpful) for this glibc enhancement request: http://sources.redhat.com/bugzilla/show_bug.cgi?id=7083 Given that glibc 2.9 was just released, presumably this won't show up until glibc 2.10, and it'll probably be a *long* time before it this will show up in real distributions, but it would be good to get this into functionality into glibc ASAP. I've been doing an analysis of which files are ending up getting fragmented on my system, and relatively common case is logfiles (since they are written via appending). Another common case is gaim log files, and of course /var/spool/mail files. All of these cases could be addressed by using fallocate() with the FALLOC_FL_KEEP_SIZE flag; and unfortunately, there is no way to do this currently through a glibc mediated interface (posix_fallocate() is mandated by the Posix specification to _not_ pass the FALLOC_FL_KEEP_SIZE flag). Changing various programs to use fallocate() when the final size of the file is known (i.e, cp, tar, cpio, rpm, etc.) helps for large files. And of course, it *definitely* helps for bittorent clients. So if the goal is to optimize filesystems aging, this would be a perfect project to sic an intern or two, or maybe an intro-level Google Summer of Code students, to sweep through some of the more common programs. For programs like cp, tar, et. al, posix_fallocate() will work just fine. For things like logrotate, we'd either need direct fallocate() support in glibc, or logrotate would have to call the system call directly, which would be evil and tricky given that different architectures use different system call numbers. (Logrotate could use fallocate to preallocate the new /var/log/syslog to same size as the previous day's syslog, which has the bonus of guaranteeing that log messages won't get lost --- and if there's not enough disk space for the fallocate to succeed, the system administrator can get notified right away, while there is still free space on the system. For paranoid DoD types who want to make sure that the audit logs are written, this could be quite useful.) If it's going to take too long to get this into glibc, I guess I could put an fallocate() interface into libe2p, although that would not be my first preference. After all, this sort of thing will be useful for all filesystems, not just ext4; it should be helpful for xfs and btrfs as well. - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
