Jens Axboe wrote:
> 
> The functionality is fine with me, merging is obviously a non-zero
> amount of cycles spent on IO and if you know it's in vain, may as well
> turn it off. One suggestion, though - if you add this as a performance
> rather than functionality change, I would suggest keeping the one-hit
> cache merge as that is essentially free. Better than free actually,
> since if you hit that merge point you'll be spending way less cycles
> than allocating+setting up a new request.
> 

With the patch below we retain the one-hit cache functionality. On a few
by-hand runs I'm seeing not much movement in the numbers (goodness). I'm
going to do a full 25 by 10-minute set of runs, and if things look OK,
I'll submit a new patch stream tomorrow.

Cheers,
Alan