Re: [PATCH] mm/madvise: keep the hardware dirty bit in MADV_COLD's THP path

[Lorenzo Stoakes (ARM)]

On Mon, Oct 12, 2026 at 02:25:38PM -0400, Samarth Narang wrote:
> Thanks both for your review into this; I was building a structural detector
> tool over page-table bit paths, and came across this.
> I got agents to reproduce it on x86 where we mark a 2MiB anon THP
> MADV_FREE, race a store from a second CPU against MADV_COLD, then force
> reclaim with MADV_PAGEOUT. The race pass loses stores while the control
> pass does not.
>
> Based on your suggestion, can we clear the accessed bit in place with
> pmdp_test_and_clear_young(), as the PTE path does via
> ptep_test_and_clear_young(), instead of rebuilding the entry from
> pmdb_invalidate()'s return value. I tried this patch on the bug, and the
> fix holds. Let me know what you think.

As I already told you, this is being handled by a member of the core team,
thanks.

--
Cheers, Lorenzo