Re: [RFC PATCH] mm: Enable khugepaged to operate on non-writable VMAs

[David Hildenbrand]

On 01.09.25 15:15, Kiryl Shutsemau wrote:
> On Mon, Sep 01, 2025 at 10:32:34AM +0200, David Hildenbrand wrote:
> > > > @@ -676,9 +676,7 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
> > > >    			writable = true;
> > > >    	}
> > > > -	if (unlikely(!writable)) {
> > > > -		result = SCAN_PAGE_RO;
> > > > -	} else if (unlikely(cc->is_khugepaged && !referenced)) {
> > > > +	if (unlikely(cc->is_khugepaged && !referenced)) {
> > > >    		result = SCAN_LACK_REFERENCED_PAGE;
> > > >    	} else {
> > > >    		result = SCAN_SUCCEED;
> > > > @@ -1421,9 +1419,7 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm,
> > > >    		     mmu_notifier_test_young(vma->vm_mm, _address)))
> > > >    			referenced++;
> > > >    	}
> > > > -	if (!writable) {
> > > > -		result = SCAN_PAGE_RO;
> > > > -	} else if (cc->is_khugepaged &&
> > > > +	if (cc->is_khugepaged &&
> > >
> > > The only practical use of the writable is gone. The only other usage is
> > > tracing which can be dropped to as it is not actionable anymore.
> > >
> > > Could you drop writable? Maybe as a separate commit.
> >
> > I think we should just do it in the same patch.
>
> Change in trace_mm_collapse_huge_page_isolate() interface doesn't belong
> to the same patch in my view.

We frequently adjust tracing code (which is specific to khugepaged in 
this case) in the same patch.

Anyhow, no strong opinion.

--
Cheers

David / dhildenb