On Wed, 2010-08-04 at 08:56 +1000, Dave Chinner wrote: > On Tue, Aug 03, 2010 at 10:34:25AM -0700, Mingming Cao wrote: > > On Fri, 2010-07-30 at 14:53 +1000, Dave Chinner wrote: > > > On Thu, Jul 29, 2010 at 08:53:24PM -0600, Matthew Wilcox wrote: > > > > On Fri, Jul 30, 2010 at 08:45:16AM +1000, Dave Chinner wrote: > > > > > If we get two unaligned direct IO's to the same filesystem block > > > > > that is marked as a new allocation (i.e. buffer_new), then both IOs will > > > > > zero the portion of the block they are not writing data to. As a > > > > > result, when the IOs complete there will be a portion of the block > > > > > that contains zeros from the last IO to complete rather than the > > > > > data that should be there. > .... > > > I don't want any direct IO for XFS to go through the page cache - > > > unaligned or not. using the page cache for the unaligned blocks > > > would also be much worse for performance that this method because it > > > turns unaligned direct IO into 3 IOs - the unaligned head block, the > > > aligned body and the unaligned tail block. It would also be a > > > performance hit you take on every single dio, whereas this way the > > > hit is only taken when an overlap is detected. > > > > Does this problem also possible for DIO and non AIO case? (Ext4 case > > this only happy with AIO+DIO+unaligned). If not, could we simply force > > unaligned AIO+DIO to be synchronous? Still direct IO... > > There is nothing specific to AIO about this bug. XFS (at least) > allows concurrent DIO writes to the same inode regardless of whether > they are dispatched via AIO or multiple separate threads and so the > race condition exists outside just the AIO context... > Okay..yeah ext4 prevent direct IO write to the same inode from multiple threads, so this is not a issue for non-aio case. How does XFS serialize direct IO (aligned) to the same file offset(or overlap) from multiple threads? Mingming -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
