It is possible for a single SGL to span an aligned boundary, eg if the SGL
is
61440 -> 90112
Then the length is 28672, which currently limits the block size to
32k. With a 32k page size the two covering blocks will be:
32768->65536 and 65536->98304
However, the correct answer is a 128K block size which will span the whole
28672 bytes in a single block.
Instead of limiting based on length figure out which high IOVA bits don't
change between the start and end addresses. That is the highest useful
page size.
Fixes: 4a35339958f1 ("RDMA/umem: Add API to find best driver supported page size in an MR")
Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
---
drivers/infiniband/core/umem.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
index 831bff8d52e547..120e98403c345d 100644
--- a/drivers/infiniband/core/umem.c
+++ b/drivers/infiniband/core/umem.c
@@ -156,8 +156,14 @@ unsigned long ib_umem_find_best_pgsz(struct ib_umem *umem,
return 0;
va = virt;
- /* max page size not to exceed MR length */
- mask = roundup_pow_of_two(umem->length);
+ /* The best result is the smallest page size that results in the minimum
+ * number of required pages. Compute the largest page size that could
+ * work based on VA address bits that don't change.
+ */
+ mask = pgsz_bitmap &
+ GENMASK(BITS_PER_LONG - 1,
+ bits_per((umem->length - 1 + umem->address) ^
+ umem->address));
/* offset into first SGL */
pgoff = umem->address & ~PAGE_MASK;
--
2.28.0
