lib/iommu-helper: skip to next segment

When a large enough area in the iommu bitmap is found but would span a
boundary we continue the search starting from the next bit position.
For large allocations this can lead to several useless invocations of
bitmap_find_next_zero_area() and iommu_is_span_boundary().

Continue the search from the start of the next segment (which is the
next bit position such that we'll not cross the same segment boundary
again).

Link: http://lkml.kernel.org/r/alpine.LFD.2.20.1606081910070.3211@schleppi
Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Reviewed-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 2 deletions

diff --git a/lib/iommu-helper.c b/lib/iommu-helper.c
index c27e269210c4..a816f3a80625 100644
--- a/lib/iommu-helper.c
+++ b/lib/iommu-helper.c
@@ -29,8 +29,7 @@ again:
         index = bitmap_find_next_zero_area(map, size, start, nr, align_mask);
         if (index < size) {
                 if (iommu_is_span_boundary(index, nr, shift, boundary_size)) {
-                        /* we could do more effectively */
-                        start = index + 1;
+                        start = ALIGN(shift + index, boundary_size) - shift;
                         goto again;
                 }
                 bitmap_set(map, index, nr);