Re: [PATCH v2 2/2] mm/mmu_gather: send tlb_remove_table_smp_sync IPI only to MM CPUs

ypodemsk
2023-06-22T13:58:35Z

On Wed, 2023-06-21 at 11:02 -0700, Nadav Amit wrote:
> > On Jun 20, 2023, at 7:46 AM, Yair Podemsky <ypodemsk@redhat.com>
> > wrote:
> >
> > @@ -1525,7 +1525,7 @@ static void collapse_and_free_pmd(struct
> > mm_struct *mm, struct vm_area_struct *v
> > addr + HPAGE_PMD_SIZE);
> > mmu_notifier_invalidate_range_start(&range);
> > pmd = pmdp_collapse_flush(vma, addr, pmdp);
> > - tlb_remove_table_sync_one();
> > + tlb_remove_table_sync_one(mm);
>
> Can’t pmdp_collapse_flush() have one additional argument
> “freed_tables”
> that it would propagate, for instance on x86 to flush_tlb_mm_range()
> ?
> Then you would not need tlb_remove_table_sync_one() to issue an
> additional
> IPI, no?
>
> It just seems that you might still have 2 IPIs in many cases instead
> of
> one, and unless I am missing something, I don’t see why.
>
Hi Nadav,
Thanks for your comment.
I think you are right and in some configurations 2 IPIs might occur.
However I a am not really dealing with the thp code at the moment,
This patch is about the mmu_gatherer and mostly dealing with IPIs sent
via the other code path.
Thanks,
Yair