Re: [RFC][PATCH 6/8] mm: handle_speculative_fault()

[Peter Zijlstra]

On Mon, 2010-01-04 at 21:10 -0800, Linus Torvalds wrote:
> Sounds doable. But it also sounds way more expensive than the current VM 
> fault handling, which is pretty close to optimal for single-threaded 
> cases.. That RCU lookup might be cheap, but just the refcount is generally 
> going to be as expensive as a lock. 

Right, that refcount adds two atomic ops, the only grace it has is that
its in the vma as opposed to the mm, but there are plenty workloads that
concentrate on a single vma, in which case you get an equally contended
cacheline as with the mmap_sem.

I was trying to avoid having to have that refcount, but then sorta
forgot about the actual fault handlers also poking at the vma :/

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/