Re: [PATCH 1/6] mm: make mm->pinned_vm an atomic64 counter

Jason Gunthorpe
2019-01-23T18:33:57Z

On Mon, Jan 21, 2019 at 09:42:15AM -0800, Davidlohr Bueso wrote:
> Taking a sleeping lock to _only_ increment a variable is quite the
> overkill, and pretty much all users do this. Furthermore, some drivers
> (ie: infiniband and scif) that need pinned semantics can go to quite
> some trouble to actually delay via workqueue (un)accounting for pinned
> pages when not possible to acquire it.
>
> By making the counter atomic we no longer need to hold the mmap_sem
> and can simply some code around it for pinned_vm users. The counter
> is 64-bit such that we need not worry about overflows such as rdma
> user input controlled from userspace.

I see a number of MM people Reviewed-by this so are we good to take
this in the RDMA tree now?

Regards,
Jason