1 files changed, 19 insertions, 0 deletions

diff --git a/include/scsi/scsi.h b/include/scsi/scsi.h
index 702fcfeb37f1..0f55f5b24896 100644
--- a/include/scsi/scsi.h
+++ b/include/scsi/scsi.h
@@ -11,6 +11,25 @@
 #include <linux/types.h>
 
 /*
+ * The maximum number of SG segments that we will put inside a
+ * scatterlist (unless chaining is used). Should ideally fit inside a
+ * single page, to avoid a higher order allocation.  We could define this
+ * to SG_MAX_SINGLE_ALLOC to pack correctly at the highest order.  The
+ * minimum value is 32
+ */
+#define SCSI_MAX_SG_SEGMENTS    128
+
+/*
+ * Like SCSI_MAX_SG_SEGMENTS, but for archs that have sg chaining. This limit
+ * is totally arbitrary, a setting of 2048 will get you at least 8mb ios.
+ */
+#ifdef ARCH_HAS_SG_CHAIN
+#define SCSI_MAX_SG_CHAIN_SEGMENTS      2048
+#else
+#define SCSI_MAX_SG_CHAIN_SEGMENTS      SCSI_MAX_SG_SEGMENTS
+#endif
+
+/*
  *      SCSI command lengths
  */