On Mon, May 20, 2013 at 03:56:07PM +0200, Jan Kara wrote: > On Thu 11-04-13 22:09:56, Jan Kara wrote: > > Writing a large file using direct IO in 16 MB chunks sometimes results > > in a pathological allocation pattern where 16 MB chunks of large free > > extent are allocated to a file in a reversed order. So extents of a file > > look for example as: > > > > ext logical physical expected length flags > > 0 0 13 4550656 > > 1 4550656 188136807 4550668 12562432 > > 2 17113088 200699240 200699238 622592 > > 3 17735680 182046055 201321831 4096 > > 4 17739776 182041959 182050150 4096 > > 5 17743872 182037863 182046054 4096 > > 6 17747968 182033767 182041958 4096 > > 7 17752064 182029671 182037862 4096 > > ... > > 6757 45400064 154381644 154389835 4096 > > 6758 45404160 154377548 154385739 4096 > > 6759 45408256 252951571 154381643 73728 eof > > > > This happens because XFS_ALLOCTYPE_THIS_BNO allocation fails (the last > > extent in the file cannot be further extended) so we fall back to > > XFS_ALLOCTYPE_NEAR_BNO allocation which picks end of a large free > > extent as the best place to continue the file. Since the chunk at the > > end of the free extent again cannot be further extended, this behavior > > repeats until the whole free extent is consumed in a reversed order. > > > > For data allocations this backward allocation isn't beneficial so make > > xfs_alloc_compute_diff() pick start of a free extent instead of its end > > for them. That avoids the backward allocation pattern. > > > > See thread at http://oss.sgi.com/archives/xfs/2013-03/msg00144.html for > > more details about the reproduction case and why this solution was > > chosen. > > > > Based on idea by Dave Chinner <dchinner@xxxxxxxxxx>. > > > > CC: Dave Chinner <dchinner@xxxxxxxxxx> > > Reviewed-by: Dave Chinner <dchinner@xxxxxxxxxx> > > Signed-off-by: Jan Kara <jack@xxxxxxx> > > --- > > fs/xfs/xfs_alloc.c | 24 ++++++++++++++++++------ > > 1 files changed, 18 insertions(+), 6 deletions(-) > > > > v2: Updated comment and commit description. > Could anybody pull this patch into XFS tree? I don't see it there... Applied. Thanks Jan. _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
