On Wed, Dec 09, 2015 at 10:22:12AM +1100, NeilBrown wrote:

quoted

+/*
+ * We only need 2 bios per I/O unit to make progress, but ensure we
+ * have a few more available to not get too tight.
+ */
+#define R5L_POOL_SIZE	1024
+

I'm really suspicious of big pool sizes.
The memory allocated to the pool is almost never used - only where no
other memory is available - so large pools are largely wasted.

I originally had 16 here, andd incremented it for some debugging that
stuck.  I retested with 4 and that works as well.  That will be included
in the next resend.