Re: [PATCH mm-new 1/3] mm/khugepaged: skip unsuitable VMAs earlier in khugepaged_scan_mm_slot()

[Kiryl Shutsemau]

On Tue, Sep 16, 2025 at 10:39:53AM +0100, Lorenzo Stoakes wrote:
> On Tue, Sep 16, 2025 at 10:29:11AM +0100, Kiryl Shutsemau wrote:
> > On Tue, Sep 16, 2025 at 02:21:26PM +0800, Lance Yang wrote:
> > > Users of mlock() expect low and predictable latency. THP collapse is a
> > > heavy operation that introduces exactly the kind of unpredictable delays
> > > they want to avoid. It has to unmap PTEs, copy data from the small folios
> > > to a new THP, and then remap the THP back to the PMD ;)
> >
> > Generally, we allow minor page faults into mlocked VMAs and avoid major.
> > This is minor page fault territory in my view.
> 
> Hm, but we won't be causing minor faults via reclaim right, since they're
> not on any LRU?

PTEs are still present when we do THP allocation. No reclaim while the
access is blocked. We only block the access on copy and PTEs->PMD
collapse.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov