Re: [PATCH] mm/thp: fix call to mmu_notifier in set_pmd_migration_entry()

[Andrea Arcangeli]

On Fri, Oct 12, 2018 at 01:35:19PM -0400, Jerome Glisse wrote:
> On Fri, Oct 12, 2018 at 01:24:22PM -0400, Andrea Arcangeli wrote:
> > Hello,
> > 
> > On Fri, Oct 12, 2018 at 12:20:54PM -0400, Zi Yan wrote:
> > > On 12 Oct 2018, at 12:09, jglisse@xxxxxxxxxx wrote:
> > > 
> > > > From: Jérôme Glisse <jglisse@xxxxxxxxxx>
> > > >
> > > > Inside set_pmd_migration_entry() we are holding page table locks and
> > > > thus we can not sleep so we can not call invalidate_range_start/end()
> > > >
> > > > So remove call to mmu_notifier_invalidate_range_start/end() and add
> > > > call to mmu_notifier_invalidate_range(). Note that we are already
> > 
> > Why the call to mmu_notifier_invalidate_range if we're under
> > range_start and followed by range_end? (it's not _range_only_end, if
> > it was _range_only_end the above would be needed)
> 
> I wanted to be extra safe and accept to over invalidate. You are right
> that it is not strictly necessary. I am fine with removing it.

If it's superfluous, I'd generally prefer strict code unless there's a
very explicit comment about it that says it's actually superfluous.
Otherwise after a while we don't know why it was added there.

> We can remove it. Should i post a v2 without it ?

That's fine with me yes.

Thanks,
Andrea