Re: [RFC PATCH 00/57] mm/collapse: rebuild collapse on migration primitives

[Kiryl Shutsemau]

On Mon, Sep 14, 2026 at 05:07:37PM +0200, David Hildenbrand (Arm) wrote:
> > As I mentioned above, we drop the ptl after the freeze. And take it a
> > second time for the install.  Allocation and the copy run in between with
> > no lock held -- on 64K the copy at PMD order is 512M of it, which is why
> > it cannot sit under either lock.
> 
> Hold on, are freezing all folios to collapse? That cannot possibly work with
> COW-shared folios that are mapped into other address spaces.

I break COW for worthy candidates in the faultin prepass before freeze,
alongside swapin. It simplifies the picture substantially. No rmap mess.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov