Re: [PATCH v6 0/5] support batch checking of references and unmapping for large folios
From: Andrew Morton <akpm@linux-foundation.org>
Date: 2026-02-10 01:53:17
Also in:
linux-mm, lkml
On Mon, 9 Feb 2026 22:07:23 +0800 Baolin Wang [off-list ref] wrote:
Currently, folio_referenced_one() always checks the young flag for each PTE sequentially, which is inefficient for large folios. This inefficiency is especially noticeable when reclaiming clean file-backed large folios, where folio_referenced() is observed as a significant performance hotspot. Moreover, on Arm architecture, which supports contiguous PTEs, there is already an optimization to clear the young flags for PTEs within a contiguous range. However, this is not sufficient. We can extend this to perform batched operations for the entire large folio (which might exceed the contiguous range: CONT_PTE_SIZE). Similar to folio_referenced_one(), we can also apply batched unmapping for large file folios to optimize the performance of file folio reclamation. By supporting batched checking of the young flags, flushing TLB entries, and unmapping, I can observed a significant performance improvements in my performance tests for file folios reclamation. Please check the performance data in the commit message of each patch.
Thanks, I updated mm.git to this version. Below is how v6 altered mm.git. I notice that this fix: https://lore.kernel.org/all/de141225-a0c1-41fd-b3e1-bcab09827ddd@linux.alibaba.com/T/#u (local) was not carried forward. Was this deliberate? Also, regarding the 80-column tricks in folio_referenced_one(): we're allowed to do this ;) unsigned long end_addr; unsigned int max_nr; end_addr = pmd_addr_end(address, vma->vm_end); max_nr = (end_addr - address) >> PAGE_SHIFT; arch/arm64/include/asm/pgtable.h | 2 +- include/linux/pgtable.h | 16 ++++++++++------ mm/rmap.c | 9 +++------ 3 files changed, 14 insertions(+), 13 deletions(-)
--- a/arch/arm64/include/asm/pgtable.h~b
+++ a/arch/arm64/include/asm/pgtable.h@@ -1843,7 +1843,7 @@ static inline int clear_flush_young_ptes unsigned long addr, pte_t *ptep, unsigned int nr) { - if (likely(nr == 1 && !pte_valid_cont(__ptep_get(ptep)))) + if (likely(nr == 1 && !pte_cont(__ptep_get(ptep)))) return __ptep_clear_flush_young(vma, addr, ptep); return contpte_clear_flush_young_ptes(vma, addr, ptep, nr); --- a/include/linux/pgtable.h~b +++ a/include/linux/pgtable.h
@@ -1070,8 +1070,8 @@ static inline void wrprotect_ptes(struct #ifndef clear_flush_young_ptes /** - * clear_flush_young_ptes - Clear the access bit and perform a TLB flush for PTEs - * that map consecutive pages of the same folio. + * clear_flush_young_ptes - Mark PTEs that map consecutive pages of the same + * folio as old and flush the TLB. * @vma: The virtual memory area the pages are mapped into. * @addr: Address the first page is mapped at. * @ptep: Page table pointer for the first entry.
@@ -1087,13 +1087,17 @@ static inline void wrprotect_ptes(struct * pages that belong to the same folio. The PTEs are all in the same PMD. */ static inline int clear_flush_young_ptes(struct vm_area_struct *vma, - unsigned long addr, pte_t *ptep, - unsigned int nr) + unsigned long addr, pte_t *ptep, unsigned int nr) { - int i, young = 0; + int young = 0; - for (i = 0; i < nr; ++i, ++ptep, addr += PAGE_SIZE) + for (;;) { young |= ptep_clear_flush_young(vma, addr, ptep); + if (--nr == 0) + break; + ptep++; + addr += PAGE_SIZE; + } return young; } --- a/mm/rmap.c~b +++ a/mm/rmap.c
@@ -963,10 +963,8 @@ static bool folio_referenced_one(struct referenced++; } else if (pvmw.pte) { if (folio_test_large(folio)) { - unsigned long end_addr = - pmd_addr_end(address, vma->vm_end); - unsigned int max_nr = - (end_addr - address) >> PAGE_SHIFT; + unsigned long end_addr = pmd_addr_end(address, vma->vm_end); + unsigned int max_nr = (end_addr - address) >> PAGE_SHIFT; pte_t pteval = ptep_get(pvmw.pte); nr = folio_pte_batch(folio, pvmw.pte,
@@ -974,8 +972,7 @@ static bool folio_referenced_one(struct } ptes += nr; - if (clear_flush_young_ptes_notify(vma, address, - pvmw.pte, nr)) + if (clear_flush_young_ptes_notify(vma, address, pvmw.pte, nr)) referenced++; /* Skip the batched PTEs */ pvmw.pte += nr - 1;
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