On 5/19/07, Eric <erpo41@xxxxxxxxx> wrote:
On Fri, 2007-05-18 at 18:36 +0530, Aneesh Kumar K.V wrote: > The reason why i am asking this is to understand the > usefulness of doing a ext4migrate followed by defrag. > [...] > Also looking at the version 0.4 I see that defrag ioctl only work if we > have EXT4_EXTENTS_FL flag set. ext4migrate is necessary because the current ext4 defrag routines will only defragment files stored as extents. AFAIK, converting a file to extents does not allow the defrag routine to defragment it "better" than an indirect block map inode, but converting any file to extents has performance benefits regardless of whether it is later defragmented. > What are the plans for making defrag work > with indirect block map inode ? I think there is a second set of patches to defragment non-extent files.
I was looking at this and didn't find the changes needed to defrag the non extent files. http://www.mail-archive.com/linux-ext4@xxxxxxxxxxxxxxx/msg01522.html
An even better defragmentation routine knows how to balance the time lost to defragmentation with the performance gained from a defragmented filesystem. IMHO, this requires detailed knowledge of the layout of a file's blocks on the disk. Right now, we get this information by looping over the FIBMAP ioctl, which I understand can take quite a long time.
With the takashi's code we use ext4_ext_alloc_blocks and see if the number of extents that we got is less than the number of extents that we have with the original file that we intent to defrag. I am not sure an ioctl is involved here. Well the intent of my mail was to find the advantage of doing an online migration. If we are not relocating the blocks corresponding to extent index then doing a online migration doesn't bring any specific performance bonus. But yes i agree that there is a performance impact with defrag by moving the data blocks closer. -aneesh - 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
