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

[Peter Xu]

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?

-- 
Peter Xu