block: set the bounce_pfn to the actual DMA limit rather than to max memory

The bounce_pfn of the request queue in 64 bit systems is set to the
current max_low_pfn. Adding more memory later makes this incorrect.
Memory allocated beyond this boot time max_low_pfn appear to require
bounce buffers (bounce buffers are actually not allocated but used in
calculating segments that may result in "over max segments limit"
errors).

Signed-off-by: Malahal Naineni <malahal@us.ibm.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/block/blk-settings.c b/block/blk-settings.c
index f8f2ddf20613..a3600a7ab8bb 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -214,7 +214,7 @@ void blk_queue_bounce_limit(struct request_queue *q, u64 dma_mask)
          */
         if (b_pfn < (min_t(u64, 0xffffffffUL, BLK_BOUNCE_HIGH) >> PAGE_SHIFT))
                 dma = 1;
-        q->limits.bounce_pfn = max_low_pfn;
+        q->limits.bounce_pfn = max(max_low_pfn, b_pfn);
 #else
         if (b_pfn < blk_max_low_pfn)
                 dma = 1;