[PATCH v5 02/11] powerpc/mm: Adds counting method to monitor lockless pgtable walks

[Christopher Lameter]

On Tue, 8 Oct 2019, Leonardo Bras wrote:

> > You are creating contention on a single exclusive cacheline. Doesnt this
> > defeat the whole purpose of the lockless page table walk? Use mmap_sem or
> > so should cause the same performance regression?
>
> Sorry, I did not understand that question.
> I mean, this is just a refcount and never causes a lock.

Locks also use atomic operations like a refcount increment. Both require
the cacheline to be in exclusive state. So the impact is very similar.