On Wed, Jun 05, 2013 at 01:30:22AM +0800, 宋柏翰 wrote: > Though what I tried to > said is that delalloc'd data will stop kjournald from writing them > back when it would like to do so, therefore those delalloc'd data will > stay in memory more longer than those non-delalloc'd ones. That's not why when you enable delayed allocation data can stay in memory longer than when delalloc is disabled (or when ext3 is used). So you were wrong about why this happens, although the observation is correct. > As described in http://lwn.net/Articles/322823/. Please note that the current behaviour vis-a-vis buffered writes and when you they will written to disk is generally true for all modern file systems: xfs, btrfs, and ext4. The workaround described at the end of the above article has been adopted by all of the modern file systems, as a workaround for buggy user space applications (which at one point included core libraries for both GNOME and KDE); this workaround however is __not__ guaranteed by POSIX, and there are other operationg systems, such as MacOS X, where you can't guarantee on these semantics. (In fact with MacOS, by default fsync() is even weaker than what POSIX guarantees; you need use fcntl(F_FULLSYNC) to get POSIX guarantees.) More context can be found here: http://blahg.josefsipek.net/?p=364 - 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
