Re: [PATCH 21/46] hugetlb: use struct hugetlb_pte for walk_hugetlb_range

[Mike Kravetz]

On 01/23/23 10:19, Peter Xu wrote:
> Hi, Mike,
> 
> On Thu, Jan 19, 2023 at 03:44:25PM -0800, Mike Kravetz wrote:
> > On 01/19/23 18:07, Peter Xu wrote:
> > > 
> > > Actually when revisiting the locks I'm getting a bit confused on whether
> > > the vma lock is needed if pmd sharing is anyway forbidden for HGM.  I
> > > raised a question in the other patch of MADV_COLLAPSE, maybe they're
> > > related questions so we can keep it there.
> > 
> > I can quickly answer that.  Yes.  The vma lock is also being used for
> > fault/truncation synchronization.  Commit e700898fa075 make sure it is
> > even used on architectures that do not support PMD sharing.
> > 
> > I had come up with a rather ugly method of using the fault mutex for
> > fault/truncation synchronization, but using the vma lock was more
> > elegant.
> 
> Thanks for answering, I'll need to read some more on truncation later.
> Before that, since COLLAPSE will already require the i_mmap_rwsem write
> lock already, does it mean it is naturally race-free against truncation
> even without vma lock?

Yes, and thanks for making me take a closer look at COLLAPSE. :)

-- 
Mike Kravetz