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
