XFS memory allocation deadlock in 2.6.38

[Sean Noonan]

> Ok, so that looks like root cause of the problem. can you try the
> patch below to see if it fixes the problem (without any other
> patches applied or reverted).

It looks like this does fix the deadlock problem.  However, it appears to come at the price of significantly higher mmap startup costs.  

# ./vmtest /xfs/hugefile.dat $(( 16 * 1024 * 1024 * 1024 ))
/xfs/d-1/hugefile.dat: mapped 17179869184 bytes in 324387362198 ticks

Sean