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

[David Hildenbrand (Arm)]

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!

-- 
Cheers,

David