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



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