Re: [PATCH v6 1/5] mm: rmap: support batched checks of the references for large folios

[Lorenzo Stoakes (Oracle)]

On Wed, Mar 25, 2026 at 03:58:36PM +0100, David Hildenbrand (Arm) wrote:
> On 3/25/26 15:36, Lorenzo Stoakes (Oracle) wrote:
> > On Mon, Mar 16, 2026 at 03:15:18PM +0100, David Hildenbrand (Arm) wrote:
> >> On 3/16/26 07:25, Baolin Wang wrote:
> >>>
> >>>
> >>>
> >>> Sure. However, after investigating RISC‑V and x86, I found that
> >>> ptep_clear_flush_young() does not flush the TLB on these architectures:
> >>>
> >>> int ptep_clear_flush_young(struct vm_area_struct *vma,
> >>>                unsigned long address, pte_t *ptep)
> >>> {
> >>>     /*
> >>>      * On x86 CPUs, clearing the accessed bit without a TLB flush
> >>>      * doesn't cause data corruption. [ It could cause incorrect
> >>>      * page aging and the (mistaken) reclaim of hot pages, but the
> >>>      * chance of that should be relatively low. ]
> >>>      *
> >>>      * So as a performance optimization don't flush the TLB when
> >>>      * clearing the accessed bit, it will eventually be flushed by
> >>>      * a context switch or a VM operation anyway. [ In the rare
> >>>      * event of it not getting flushed for a long time the delay
> >>>      * shouldn't really matter because there's no real memory
> >>>      * pressure for swapout to react to. ]
> >>>      */
> >>>     return ptep_test_and_clear_young(vma, address, ptep);
> >>> }
> >>
> >> You'd probably want an arch helper then, that tells you whether
> >> a flush_tlb_range() after ptep_test_and_clear_young() is required.
> >>
> >> Or some special flush_tlb_range() helper.
> >>
> >> I agree that it requires more work.
> >
> > Sorry unclear here - does the series need more work or does a follow up patch
> > need more work?
>
> Follow up!

Ok good as in mm-stable now. Sadly means I don't get to review it but there we
go.

>
> --
> Cheers,
>
> David

Thanks, Lorenzo