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

On Fri, 24 Aug 2018 13:39:53 +0200
Peter Zijlstra [off-list ref] wrote:

On Fri, Aug 24, 2018 at 01:32:14PM +0200, Peter Zijlstra wrote:

quoted

On Fri, Aug 24, 2018 at 10:47:17AM +0200, Peter Zijlstra wrote:  

quoted

On Thu, Aug 23, 2018 at 02:39:59PM +0100, Will Deacon wrote:  

quoted

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")  

Ah, good, it seems that already got cleaned up a lot. But it all moved
into the power code.. blergh.

I lost track of what the problem is here?

For powerpc, tlb_start_vma is not the right API to use for this because
it wants to deal with different page sizes within a vma.

Thanks,
Nick