On Thu, Jul 19, 2018 at 10:15 AM, Rik van Riel <[email protected]> wrote: > > > Given that CPUs in lazy TLB mode stay part of the mm_cpumask, > that WARN_ON seems misplaced. You are right though, that the > mm_cpumask alone should provide enough information for us to > avoid a need for both tsk->active_mm and the refcounting. >
If you do this extra shootdown after freeing pagetables, it would be odd if mm_cpumask() wasn't empty. But you're right, the warn is probably silly. And if you move it into arch_exit_mmap(), the warn is definitely wrong. > > Does all that make sense? Basically, as I understand it, the > expensive atomic ops you're seeing are all pointless because they're > enabling an optimization that hasn't actually worked for a long time, > if ever. > > > Our benchmark results suggest that lazy TLB mode works, and makes > a measurable performance difference. Getting rid of the atomic ops > should make it a little better, though :) > I'm not saying lazy mode is useless. I'm saying that active_mm isn't needed for x86's lazy mode :)
