From: Dev Jain Date: Tue, 10 Jun 2025 03:50:43 +0000 (+0530) Subject: mm: optimize mremap() by PTE batching X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f822a9a81a31311d67f260aea96005540b18ab07;p=thirdparty%2Flinux.git mm: optimize mremap() by PTE batching Use folio_pte_batch() to optimize move_ptes(). On arm64, if the ptes are painted with the contig bit, then ptep_get() will iterate through all 16 entries to collect a/d bits. Hence this optimization will result in a 16x reduction in the number of ptep_get() calls. Next, ptep_get_and_clear() will eventually call contpte_try_unfold() on every contig block, thus flushing the TLB for the complete large folio range. Instead, use get_and_clear_full_ptes() so as to elide TLBIs on each contig block, and only do them on the starting and ending contig block. For split folios, there will be no pte batching; nr_ptes will be 1. For pagetable splitting, the ptes will still point to the same large folio; for arm64, this results in the optimization described above, and for other arches (including the general case), a minor improvement is expected due to a reduction in the number of function calls. Link: https://lkml.kernel.org/r/20250610035043.75448-3-dev.jain@arm.com Signed-off-by: Dev Jain Reviewed-by: Barry Song Reviewed-by: Lorenzo Stoakes Reviewed-by: Pedro Falcato Cc: Anshuman Khandual Cc: Bang Li Cc: Baolin Wang Cc: bibo mao Cc: David Hildenbrand Cc: Hugh Dickins Cc: Ingo Molnar Cc: Jann Horn Cc: Lance Yang Cc: Liam Howlett Cc: Matthew Wilcox (Oracle) Cc: Peter Xu Cc: Qi Zheng Cc: Ryan Roberts Cc: Vlastimil Babka Cc: Yang Shi Cc: Zi Yan Signed-off-by: Andrew Morton --- diff --git a/mm/mremap.c b/mm/mremap.c index 180b12225368e..18b215521adae 100644 --- a/mm/mremap.c +++ b/mm/mremap.c @@ -170,6 +170,23 @@ static pte_t move_soft_dirty_pte(pte_t pte) return pte; } +static int mremap_folio_pte_batch(struct vm_area_struct *vma, unsigned long addr, + pte_t *ptep, pte_t pte, int max_nr) +{ + const fpb_t flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY; + struct folio *folio; + + if (max_nr == 1) + return 1; + + folio = vm_normal_folio(vma, addr, pte); + if (!folio || !folio_test_large(folio)) + return 1; + + return folio_pte_batch(folio, addr, ptep, pte, max_nr, flags, NULL, + NULL, NULL); +} + static int move_ptes(struct pagetable_move_control *pmc, unsigned long extent, pmd_t *old_pmd, pmd_t *new_pmd) { @@ -177,7 +194,7 @@ static int move_ptes(struct pagetable_move_control *pmc, bool need_clear_uffd_wp = vma_has_uffd_without_event_remap(vma); struct mm_struct *mm = vma->vm_mm; pte_t *old_ptep, *new_ptep; - pte_t pte; + pte_t old_pte, pte; pmd_t dummy_pmdval; spinlock_t *old_ptl, *new_ptl; bool force_flush = false; @@ -185,6 +202,8 @@ static int move_ptes(struct pagetable_move_control *pmc, unsigned long new_addr = pmc->new_addr; unsigned long old_end = old_addr + extent; unsigned long len = old_end - old_addr; + int max_nr_ptes; + int nr_ptes; int err = 0; /* @@ -236,14 +255,16 @@ static int move_ptes(struct pagetable_move_control *pmc, flush_tlb_batched_pending(vma->vm_mm); arch_enter_lazy_mmu_mode(); - for (; old_addr < old_end; old_ptep++, old_addr += PAGE_SIZE, - new_ptep++, new_addr += PAGE_SIZE) { + for (; old_addr < old_end; old_ptep += nr_ptes, old_addr += nr_ptes * PAGE_SIZE, + new_ptep += nr_ptes, new_addr += nr_ptes * PAGE_SIZE) { VM_WARN_ON_ONCE(!pte_none(*new_ptep)); - if (pte_none(ptep_get(old_ptep))) + nr_ptes = 1; + max_nr_ptes = (old_end - old_addr) >> PAGE_SHIFT; + old_pte = ptep_get(old_ptep); + if (pte_none(old_pte)) continue; - pte = ptep_get_and_clear(mm, old_addr, old_ptep); /* * If we are remapping a valid PTE, make sure * to flush TLB before we drop the PTL for the @@ -255,8 +276,12 @@ static int move_ptes(struct pagetable_move_control *pmc, * the TLB entry for the old mapping has been * flushed. */ - if (pte_present(pte)) + if (pte_present(old_pte)) { + nr_ptes = mremap_folio_pte_batch(vma, old_addr, old_ptep, + old_pte, max_nr_ptes); force_flush = true; + } + pte = get_and_clear_full_ptes(mm, old_addr, old_ptep, nr_ptes, 0); pte = move_pte(pte, old_addr, new_addr); pte = move_soft_dirty_pte(pte); @@ -269,7 +294,7 @@ static int move_ptes(struct pagetable_move_control *pmc, else if (is_swap_pte(pte)) pte = pte_swp_clear_uffd_wp(pte); } - set_pte_at(mm, new_addr, new_ptep, pte); + set_ptes(mm, new_addr, new_ptep, pte, nr_ptes); } }