From 19eaf44954df64f9bc8dec398219e15ad0811497 Mon Sep 17 00:00:00 2001 From: Ryan Roberts Date: Thu, 7 Dec 2023 16:12:05 +0000 Subject: mm: thp: support allocation of anonymous multi-size THP Introduce the logic to allow THP to be configured (through the new sysfs interface we just added) to allocate large folios to back anonymous memory, which are larger than the base page size but smaller than PMD-size. We call this new THP extension "multi-size THP" (mTHP). mTHP continues to be PTE-mapped, but in many cases can still provide similar benefits to traditional PMD-sized THP: Page faults are significantly reduced (by a factor of e.g. 4, 8, 16, etc. depending on the configured order), but latency spikes are much less prominent because the size of each page isn't as huge as the PMD-sized variant and there is less memory to clear in each page fault. The number of per-page operations (e.g. ref counting, rmap management, lru list management) are also significantly reduced since those ops now become per-folio. Some architectures also employ TLB compression mechanisms to squeeze more entries in when a set of PTEs are virtually and physically contiguous and approporiately aligned. In this case, TLB misses will occur less often. The new behaviour is disabled by default, but can be enabled at runtime by writing to /sys/kernel/mm/transparent_hugepage/hugepage-XXkb/enabled (see documentation in previous commit). The long term aim is to change the default to include suitable lower orders, but there are some risks around internal fragmentation that need to be better understood first. [ryan.roberts@arm.com: resolve some multi-size THP review nits] Link: https://lkml.kernel.org/r/20231214160251.3574571-1-ryan.roberts@arm.com Link: https://lkml.kernel.org/r/20231207161211.2374093-5-ryan.roberts@arm.com Signed-off-by: Ryan Roberts Tested-by: Kefeng Wang Tested-by: John Hubbard Acked-by: David Hildenbrand Cc: Alistair Popple Cc: Anshuman Khandual Cc: Barry Song Cc: Catalin Marinas Cc: David Rientjes Cc: "Huang, Ying" Cc: Hugh Dickins Cc: Itaru Kitayama Cc: Kirill A. Shutemov Cc: Luis Chamberlain Cc: Matthew Wilcox (Oracle) Cc: Vlastimil Babka Cc: Yang Shi Cc: Yin Fengwei Cc: Yu Zhao Cc: Zi Yan Signed-off-by: Andrew Morton --- mm/memory.c | 109 +++++++++++++++++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 100 insertions(+), 9 deletions(-) (limited to 'mm') diff --git a/mm/memory.c b/mm/memory.c index 8ab2d994d997..3c530b639559 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -4125,6 +4125,84 @@ out_release: return ret; } +static bool pte_range_none(pte_t *pte, int nr_pages) +{ + int i; + + for (i = 0; i < nr_pages; i++) { + if (!pte_none(ptep_get_lockless(pte + i))) + return false; + } + + return true; +} + +static struct folio *alloc_anon_folio(struct vm_fault *vmf) +{ +#ifdef CONFIG_TRANSPARENT_HUGEPAGE + struct vm_area_struct *vma = vmf->vma; + unsigned long orders; + struct folio *folio; + unsigned long addr; + pte_t *pte; + gfp_t gfp; + int order; + + /* + * If uffd is active for the vma we need per-page fault fidelity to + * maintain the uffd semantics. + */ + if (unlikely(userfaultfd_armed(vma))) + goto fallback; + + /* + * Get a list of all the (large) orders below PMD_ORDER that are enabled + * for this vma. Then filter out the orders that can't be allocated over + * the faulting address and still be fully contained in the vma. + */ + orders = thp_vma_allowable_orders(vma, vma->vm_flags, false, true, true, + BIT(PMD_ORDER) - 1); + orders = thp_vma_suitable_orders(vma, vmf->address, orders); + + if (!orders) + goto fallback; + + pte = pte_offset_map(vmf->pmd, vmf->address & PMD_MASK); + if (!pte) + return ERR_PTR(-EAGAIN); + + /* + * Find the highest order where the aligned range is completely + * pte_none(). Note that all remaining orders will be completely + * pte_none(). + */ + order = highest_order(orders); + while (orders) { + addr = ALIGN_DOWN(vmf->address, PAGE_SIZE << order); + if (pte_range_none(pte + pte_index(addr), 1 << order)) + break; + order = next_order(&orders, order); + } + + pte_unmap(pte); + + /* Try allocating the highest of the remaining orders. */ + gfp = vma_thp_gfp_mask(vma); + while (orders) { + addr = ALIGN_DOWN(vmf->address, PAGE_SIZE << order); + folio = vma_alloc_folio(gfp, order, vma, addr, true); + if (folio) { + clear_huge_page(&folio->page, vmf->address, 1 << order); + return folio; + } + order = next_order(&orders, order); + } + +fallback: +#endif + return vma_alloc_zeroed_movable_folio(vmf->vma, vmf->address); +} + /* * We enter with non-exclusive mmap_lock (to exclude vma changes, * but allow concurrent faults), and pte mapped but not yet locked. @@ -4134,9 +4212,12 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf) { bool uffd_wp = vmf_orig_pte_uffd_wp(vmf); struct vm_area_struct *vma = vmf->vma; + unsigned long addr = vmf->address; struct folio *folio; vm_fault_t ret = 0; + int nr_pages = 1; pte_t entry; + int i; /* File mapping without ->vm_ops ? */ if (vma->vm_flags & VM_SHARED) @@ -4176,10 +4257,16 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf) /* Allocate our own private page. */ if (unlikely(anon_vma_prepare(vma))) goto oom; - folio = vma_alloc_zeroed_movable_folio(vma, vmf->address); + /* Returns NULL on OOM or ERR_PTR(-EAGAIN) if we must retry the fault */ + folio = alloc_anon_folio(vmf); + if (IS_ERR(folio)) + return 0; if (!folio) goto oom; + nr_pages = folio_nr_pages(folio); + addr = ALIGN_DOWN(vmf->address, nr_pages * PAGE_SIZE); + if (mem_cgroup_charge(folio, vma->vm_mm, GFP_KERNEL)) goto oom_free_page; folio_throttle_swaprate(folio, GFP_KERNEL); @@ -4196,12 +4283,15 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf) if (vma->vm_flags & VM_WRITE) entry = pte_mkwrite(pte_mkdirty(entry), vma); - vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, vmf->address, - &vmf->ptl); + vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, addr, &vmf->ptl); if (!vmf->pte) goto release; - if (vmf_pte_changed(vmf)) { - update_mmu_tlb(vma, vmf->address, vmf->pte); + if (nr_pages == 1 && vmf_pte_changed(vmf)) { + update_mmu_tlb(vma, addr, vmf->pte); + goto release; + } else if (nr_pages > 1 && !pte_range_none(vmf->pte, nr_pages)) { + for (i = 0; i < nr_pages; i++) + update_mmu_tlb(vma, addr + PAGE_SIZE * i, vmf->pte + i); goto release; } @@ -4216,16 +4306,17 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf) return handle_userfault(vmf, VM_UFFD_MISSING); } - inc_mm_counter(vma->vm_mm, MM_ANONPAGES); - folio_add_new_anon_rmap(folio, vma, vmf->address); + folio_ref_add(folio, nr_pages - 1); + add_mm_counter(vma->vm_mm, MM_ANONPAGES, nr_pages); + folio_add_new_anon_rmap(folio, vma, addr); folio_add_lru_vma(folio, vma); setpte: if (uffd_wp) entry = pte_mkuffd_wp(entry); - set_pte_at(vma->vm_mm, vmf->address, vmf->pte, entry); + set_ptes(vma->vm_mm, addr, vmf->pte, entry, nr_pages); /* No need to invalidate - it was non-present before */ - update_mmu_cache_range(vmf, vma, vmf->address, vmf->pte, 1); + update_mmu_cache_range(vmf, vma, addr, vmf->pte, nr_pages); unlock: if (vmf->pte) pte_unmap_unlock(vmf->pte, vmf->ptl); -- cgit v1.2.3