Re: [PATCH v6 6/7] mm: fix MADV_[FREE|DONTNEED] TLB flush miss problem

[Minchan Kim]

Hi Peter,

On Fri, Aug 11, 2017 at 03:30:20PM +0200, Peter Zijlstra wrote:
> On Tue, Aug 01, 2017 at 05:08:17PM -0700, Nadav Amit wrote:
> >  void tlb_finish_mmu(struct mmu_gather *tlb,
> >  		unsigned long start, unsigned long end)
> >  {
> > -	arch_tlb_finish_mmu(tlb, start, end);
> > +	/*
> > +	 * If there are parallel threads are doing PTE changes on same range
> > +	 * under non-exclusive lock(e.g., mmap_sem read-side) but defer TLB
> > +	 * flush by batching, a thread has stable TLB entry can fail to flush
> > +	 * the TLB by observing pte_none|!pte_dirty, for example so flush TLB
> > +	 * forcefully if we detect parallel PTE batching threads.
> > +	 */
> > +	bool force = mm_tlb_flush_nested(tlb->mm);
> > +
> > +	arch_tlb_finish_mmu(tlb, start, end, force);
> >  }
> 
> I don't understand the comment nor the ordering. What guarantees we see
> the increment if we need to?

How about this about commenting part?