block: fix queue bounce limit setting

Impact: don't set GFP_DMA in q->bounce_gfp unnecessarily

All DMA address limits are expressed in terms of the last addressable
unit (byte or page) instead of one plus that.  However, when
determining bounce_gfp for 64bit machines in blk_queue_bounce_limit(),
it compares the specified limit against 0x100000000UL to determine
whether it's below 4G ending up falsely setting GFP_DMA in
q->bounce_gfp.

As DMA zone is very small on x86_64, this makes larger SG_IO transfers
very eager to trigger OOM killer.  Fix it.  While at it, rename the
parameter to @dma_mask for clarity and convert comment to proper
winged style.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 11 insertions, 9 deletions

diff --git a/block/blk-settings.c b/block/blk-settings.c
index 69c42adde52b..57af728d94bb 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -156,26 +156,28 @@ EXPORT_SYMBOL(blk_queue_make_request);
 
 /**
  * blk_queue_bounce_limit - set bounce buffer limit for queue
- * @q:  the request queue for the device
- * @dma_addr:   bus address limit
+ * @q: the request queue for the device
+ * @dma_mask: the maximum address the device can handle
  *
  * Description:
  *    Different hardware can have different requirements as to what pages
  *    it can do I/O directly to. A low level driver can call
  *    blk_queue_bounce_limit to have lower memory pages allocated as bounce
- *    buffers for doing I/O to pages residing above @dma_addr.
+ *    buffers for doing I/O to pages residing above @dma_mask.
  **/
-void blk_queue_bounce_limit(struct request_queue *q, u64 dma_addr)
+void blk_queue_bounce_limit(struct request_queue *q, u64 dma_mask)
 {
-        unsigned long b_pfn = dma_addr >> PAGE_SHIFT;
+        unsigned long b_pfn = dma_mask >> PAGE_SHIFT;
         int dma = 0;
 
         q->bounce_gfp = GFP_NOIO;
 #if BITS_PER_LONG == 64
-        /* Assume anything <= 4GB can be handled by IOMMU.
-           Actually some IOMMUs can handle everything, but I don't
-           know of a way to test this here. */
-        if (b_pfn < (min_t(u64, 0x100000000UL, BLK_BOUNCE_HIGH) >> PAGE_SHIFT))
+        /*
+         * Assume anything <= 4GB can be handled by IOMMU.  Actually
+         * some IOMMUs can handle everything, but I don't know of a
+         * way to test this here.
+         */
+        if (b_pfn < (min_t(u64, 0xffffffffUL, BLK_BOUNCE_HIGH) >> PAGE_SHIFT))
                 dma = 1;
         q->bounce_pfn = max_low_pfn;
 #else