On Tue, 2011-01-04 at 15:48 +1100, Dave Chinner wrote: > From: Dave Chinner <dchinner@xxxxxxxxxx> > > When two concurrent unaligned, non-overlapping direct IOs are issued > to the same block, the direct Io layer will race to zero the block. > The result is that one of the concurrent IOs will overwrite data > written by the other IO with zeros. This is demonstrated by the > xfsqa test 240. > > To avoid this problem, serialise all unaligned direct IOs to an > inode with a big hammer. We need a big hammer approach as we need to > serialise AIO as well, so we can't just block writes on locks. > Hence, the big hammer is calling xfs_ioend_wait() while holding out > other unaligned direct IOs from starting. > > We don't bother trying to serialised aligned vs unaligned IOs as > they are overlapping IO and the result of concurrent overlapping IOs > is undefined - the result of either IO is a valid result so we let > them race. Hence we only penalise unaligned IO, which already has a > major overhead compared to aligned IO so this isn't a major problem. Wow, after the rest of this series it gets easy! Looks good. Reviewed-by: Alex Elder <aelder@xxxxxxx> > Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx> > --- > fs/xfs/linux-2.6/xfs_file.c | 28 ++++++++++++++++++++++++---- > 1 files changed, 24 insertions(+), 4 deletions(-) _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
