On Wednesday 03 Jun 2015 12:41:02 David Sterba wrote: > On Wed, Jun 03, 2015 at 02:59:54PM +0530, Chandan Rajendra wrote: > > max_to_defrag represents the number of pages to defrag rather than the > > last > > page of the file range to be defragged. Fix this. > > Please update the changelog and describe the buggy behaviour. From a > brief look I think that the defrag batch will be much higher than > desired. Elsewhere the defrag batch is 1024, the page indexes used here > are always large numbers. I guess this could (partially) explain high > load during defrag that people report. > > ACK for the fix, I'll stick a reviewed-by to v2. Hello Dave, Consider a file having 10 4k blocks (i.e. blocks in the range [0 - 9]). If the defrag ioctl was invoked for the block range [3 - 6], then max_to_defrag should actually have the value 4. Instead in the current code we end up setting it to 6. Now, this does not (yet) cause an issue since the first part of the while loop condition in btrfs_defrag_file() (i.e. "i <= last_index") causes the control to flow out of the while loop before any buggy behavior is actually caused. So the patch just makes sure that max_to_defrag ends up having the right value rather than fixing a bug. I did run the xfstests suite to make sure that no new regressions were introduced by this patch. -- chandan -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
