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From: Sebastian Ott <sebott@linux.vnet.ibm.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com>,
	linux-kernel@vger.kernel.org
Subject: [PATCH] lib/iommu-helper: skip to next segment
Date: Wed, 8 Jun 2016 19:11:58 +0200 (CEST)
Message-ID: <alpine.LFD.2.20.1606081910070.3211@schleppi> (raw)

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).

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Reviewed-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
---
 lib/iommu-helper.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/lib/iommu-helper.c b/lib/iommu-helper.c
index c27e269..a816f3a 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);
-- 
2.3.0

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