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

From: Nadav Amit
Date: Fri Aug 24 2018 - 13:28:27 EST

at 1:47 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> 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.

Somewhat unrelated, but I use this opportunity that TLB got your attention
for something that bothers me for some time. clear_fixmap(), which is used
in various places (e.g., text_poke()), ends up in doing only a local TLB
flush (in __set_pte_vaddr()).

Is that sufficient?