On 10/31/2012 07:31 PM, David Sterba wrote: > On Wed, Oct 31, 2012 at 10:30:22AM +0800, Jeff Liu wrote: >> One idea is to mark those cloned extents as FIEMAP_EXTENT_SHARED so that >> we can go through a file to figure out how many extents are shared >> through fiemap(2), and calculate the real storage(fs/subvolume) footprint >> in the end. > > This will cost at least one more seek per extent to find out that the > extent is shared, could be quite expensive. I propose this because OCFS2 report shared space in this way combine with du(1).
An old patch set to teach du(1) aware of reflinked file: https://oss.oracle.com/pipermail/ocfs2-devel/2010-September/007293.html Do you means that the costs is very expensive for userland extent status checkup per file? If yes, I have once tested an 50Gb OCFS2 partition filled with reflinked files on an old laptop, it spent around 4 minutes to show the totally results if I recalled correct, but this definitely depending on the real world scenarios. > And without any possibility to turn this off,I'm afraid this will render > FIEMAP unusable in practice. For OCFS2, the FIEMAP_EXTENT_SHARED flag will be set upon fiemap ioctl(2) if an extent is OCFS2_EXT_REFCOUNTED(i.e. reflinked or cloned), which means that FIEMAP_EXTENT_SHARED is not a persistent flag, but I have no idea how Btrfs would be in this point. :( Thanks, -Jeff > > david > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
