On Wed, 22 Aug 2012 11:57:02 +0800 Yuanhan Liu [off-list ref]
wrote:

 
-#define NR_STRIPES		256
+#define NR_STRIPES		1024

Changing one magic number into another magic number might help your case, but
it not really a general solution.

Possibly making sure that max_nr_stripes is at least some multiple of the
chunk size might make sense, but I wouldn't want to see a very large multiple.

I thing the problems with RAID5 are deeper than that.  Hopefully I'll figure
out exactly what the best fix is soon - I'm trying to look into it.

I don't think the size of the cache is a big part of the solution.  I think
correct scheduling of IO is the real answer.

Thanks,
NeilBrown