Re: [PATCH v6 1/5] mm: rmap: support batched checks of the references for large folios
From: Baolin Wang <baolin.wang@linux.alibaba.com>
Date: 2026-03-26 01:48:01
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On 3/25/26 11:06 PM, Lorenzo Stoakes (Oracle) wrote:
On Wed, Mar 25, 2026 at 03:58:36PM +0100, David Hildenbrand (Arm) wrote:quoted
On 3/25/26 15:36, Lorenzo Stoakes (Oracle) wrote:quoted
On Mon, Mar 16, 2026 at 03:15:18PM +0100, David Hildenbrand (Arm) wrote:quoted
On 3/16/26 07:25, Baolin Wang wrote:quoted
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, David. I forgot to reply to your email because I've had a lot to sort out recently.) Rather than adding more arch helpers (we already have plenty for the young flag check), I think we should try removing the TLB flush, as I mentioned to Barry[1]. MGLRU reclaim already skips the TLB flush, and it seems to work fine. What do you think? Here are our previous attempts to remove the TLB flush: My patch: https://lkml.org/lkml/2023/10/24/533 Barry's patch: https://lore.kernel.org/lkml/20220617070555.344368-1-21cnbao@gmail.com/ (local) [1] https://lore.kernel.org/all/6bdc4b03-9631-4717-a3fa-2785a7930aba@linux.alibaba.com/ (local)
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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.
Actually this patchset has already been merged upstream:)