RE: [PATCH] likely cleanup: revert unlikely in ll_back_merge_fn

[Hua Zhong]

It seems that new BIOs do not have BIO_SEG_VALID set. So when you do sequential IO, the IO being back-merged should always have not
had valid segments.

I ran bonnie++ and it shows the same thing.

> Well you'd want to optimize for the busy case, right, no 
> point in optimizing for a more idle system.
> 
> I'm not at all uninterested in this, I'd just like to see a 
> more intelligent/controlled work load that actually stresses 
> the io subsystem being profiled. If you have a not-so-busy 
> system, you like don't do enough IO to trigger a lot of 
> merges. Or maybe you do, and we just have a bug somewhere so 
> that we unfortunately repeatedly recount segments.
> 
> Care to run a simple io benchmark and profile that?
> 
> --
> Jens Axboe
> 

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