Re: [PATCH 3/4] mm/tlb, x86/mm: Support invalidating TLB caches for RCU_TABLE_FREE

[Peter Zijlstra]

On Fri, Aug 24, 2018 at 10:47:17AM +0200, Peter Zijlstra wrote:
> On Thu, Aug 23, 2018 at 02:39:59PM +0100, Will Deacon wrote:
> > The only problem with this approach is that we've lost track of the granule
> > size by the point we get to the tlb_flush(), so we can't adjust the stride of
> > the TLB invalidations for huge mappings, which actually works nicely in the
> > synchronous case (e.g. we perform a single invalidation for a 2MB mapping,
> > rather than iterating over it at a 4k granule).
> > 
> > One thing we could do is switch to synchronous mode if we detect a change in
> > granule (i.e. treat it like a batch failure).
> 
> We could use tlb_start_vma() to track that, I think. Shouldn't be too
> hard.

Hurm.. look at commit:

  e77b0852b551 ("mm/mmu_gather: track page size with mmu gather and force flush if page size change")

yuck yuck yuck. That needs fixing.