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([2a02:6b67:d752:5f00:c46:86ac:45ea:7590]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38f259f8217sm13365164f8f.90.2025.02.17.12.55.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 17 Feb 2025 12:55:12 -0800 (PST) Message-ID: Date: Mon, 17 Feb 2025 20:55:11 +0000 Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC v2 7/9] khugepaged: add mTHP support To: Nico Pache , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-mm@kvack.org Cc: ryan.roberts@arm.com, anshuman.khandual@arm.com, catalin.marinas@arm.com, cl@gentwo.org, vbabka@suse.cz, mhocko@suse.com, apopple@nvidia.com, dave.hansen@linux.intel.com, will@kernel.org, baohua@kernel.org, jack@suse.cz, srivatsa@csail.mit.edu, haowenchao22@gmail.com, hughd@google.com, aneesh.kumar@kernel.org, yang@os.amperecomputing.com, peterx@redhat.com, ioworker0@gmail.com, wangkefeng.wang@huawei.com, ziy@nvidia.com, jglisse@google.com, surenb@google.com, vishal.moola@gmail.com, zokeefe@google.com, zhengqi.arch@bytedance.com, jhubbard@nvidia.com, 21cnbao@gmail.com, willy@infradead.org, kirill.shutemov@linux.intel.com, david@redhat.com, aarcange@redhat.com, raquini@redhat.com, dev.jain@arm.com, sunnanyong@huawei.com, audra@redhat.com, akpm@linux-foundation.org, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, tiwai@suse.de References: <20250211003028.213461-1-npache@redhat.com> <20250211003028.213461-8-npache@redhat.com> Content-Language: en-US From: Usama Arif In-Reply-To: <20250211003028.213461-8-npache@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/02/2025 00:30, Nico Pache wrote: > Introduce the ability for khugepaged to collapse to different mTHP sizes. > While scanning a PMD range for potential collapse candidates, keep track > of pages in MIN_MTHP_ORDER chunks via a bitmap. Each bit represents a > utilized region of order MIN_MTHP_ORDER ptes. We remove the restriction > of max_ptes_none during the scan phase so we dont bailout early and miss > potential mTHP candidates. > > After the scan is complete we will perform binary recursion on the > bitmap to determine which mTHP size would be most efficient to collapse > to. max_ptes_none will be scaled by the attempted collapse order to > determine how full a THP must be to be eligible. > > If a mTHP collapse is attempted, but contains swapped out, or shared > pages, we dont perform the collapse. > > Signed-off-by: Nico Pache > --- > mm/khugepaged.c | 122 ++++++++++++++++++++++++++++++++---------------- > 1 file changed, 83 insertions(+), 39 deletions(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index c8048d9ec7fb..cd310989725b 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -1127,13 +1127,14 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address, > { > LIST_HEAD(compound_pagelist); > pmd_t *pmd, _pmd; > - pte_t *pte; > + pte_t *pte, mthp_pte; > pgtable_t pgtable; > struct folio *folio; > spinlock_t *pmd_ptl, *pte_ptl; > int result = SCAN_FAIL; > struct vm_area_struct *vma; > struct mmu_notifier_range range; > + unsigned long _address = address + offset * PAGE_SIZE; > VM_BUG_ON(address & ~HPAGE_PMD_MASK); > > /* > @@ -1148,12 +1149,13 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address, > *mmap_locked = false; > } > > - result = alloc_charge_folio(&folio, mm, cc, HPAGE_PMD_ORDER); > + result = alloc_charge_folio(&folio, mm, cc, order); > if (result != SCAN_SUCCEED) > goto out_nolock; > > mmap_read_lock(mm); > - result = hugepage_vma_revalidate(mm, address, true, &vma, cc, HPAGE_PMD_ORDER); > + *mmap_locked = true; > + result = hugepage_vma_revalidate(mm, address, true, &vma, cc, order); > if (result != SCAN_SUCCEED) { > mmap_read_unlock(mm); > goto out_nolock; > @@ -1171,13 +1173,14 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address, > * released when it fails. So we jump out_nolock directly in > * that case. Continuing to collapse causes inconsistency. > */ > - result = __collapse_huge_page_swapin(mm, vma, address, pmd, > - referenced, HPAGE_PMD_ORDER); > + result = __collapse_huge_page_swapin(mm, vma, _address, pmd, > + referenced, order); > if (result != SCAN_SUCCEED) > goto out_nolock; > } > > mmap_read_unlock(mm); > + *mmap_locked = false; > /* > * Prevent all access to pagetables with the exception of > * gup_fast later handled by the ptep_clear_flush and the VM > @@ -1187,7 +1190,7 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address, > * mmap_lock. > */ > mmap_write_lock(mm); > - result = hugepage_vma_revalidate(mm, address, true, &vma, cc, HPAGE_PMD_ORDER); > + result = hugepage_vma_revalidate(mm, address, true, &vma, cc, order); > if (result != SCAN_SUCCEED) > goto out_up_write; > /* check if the pmd is still valid */ > @@ -1198,11 +1201,12 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address, > vma_start_write(vma); > anon_vma_lock_write(vma->anon_vma); > > - mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm, address, > - address + HPAGE_PMD_SIZE); > + mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm, _address, > + _address + (PAGE_SIZE << order)); > mmu_notifier_invalidate_range_start(&range); > > pmd_ptl = pmd_lock(mm, pmd); /* probably unnecessary */ > + > /* > * This removes any huge TLB entry from the CPU so we won't allow > * huge and small TLB entries for the same virtual address to > @@ -1216,10 +1220,10 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address, > mmu_notifier_invalidate_range_end(&range); > tlb_remove_table_sync_one(); > > - pte = pte_offset_map_lock(mm, &_pmd, address, &pte_ptl); > + pte = pte_offset_map_lock(mm, &_pmd, _address, &pte_ptl); > if (pte) { > - result = __collapse_huge_page_isolate(vma, address, pte, cc, > - &compound_pagelist, HPAGE_PMD_ORDER); > + result = __collapse_huge_page_isolate(vma, _address, pte, cc, > + &compound_pagelist, order); > spin_unlock(pte_ptl); > } else { > result = SCAN_PMD_NULL; > @@ -1248,8 +1252,8 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address, > anon_vma_unlock_write(vma->anon_vma); > > result = __collapse_huge_page_copy(pte, folio, pmd, _pmd, > - vma, address, pte_ptl, > - &compound_pagelist, HPAGE_PMD_ORDER); > + vma, _address, pte_ptl, > + &compound_pagelist, order); > pte_unmap(pte); > if (unlikely(result != SCAN_SUCCEED)) > goto out_up_write; > @@ -1260,20 +1264,37 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address, > * write. > */ > __folio_mark_uptodate(folio); > - pgtable = pmd_pgtable(_pmd); > - > - _pmd = mk_huge_pmd(&folio->page, vma->vm_page_prot); > - _pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma); > - > - spin_lock(pmd_ptl); > - BUG_ON(!pmd_none(*pmd)); > - folio_add_new_anon_rmap(folio, vma, address, RMAP_EXCLUSIVE); > - folio_add_lru_vma(folio, vma); > - pgtable_trans_huge_deposit(mm, pmd, pgtable); > - set_pmd_at(mm, address, pmd, _pmd); > - update_mmu_cache_pmd(vma, address, pmd); > - deferred_split_folio(folio, false); > - spin_unlock(pmd_ptl); > + if (order == HPAGE_PMD_ORDER) { > + pgtable = pmd_pgtable(_pmd); > + _pmd = mk_huge_pmd(&folio->page, vma->vm_page_prot); > + _pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma); > + > + spin_lock(pmd_ptl); > + BUG_ON(!pmd_none(*pmd)); > + folio_add_new_anon_rmap(folio, vma, _address, RMAP_EXCLUSIVE); > + folio_add_lru_vma(folio, vma); > + pgtable_trans_huge_deposit(mm, pmd, pgtable); > + set_pmd_at(mm, address, pmd, _pmd); > + update_mmu_cache_pmd(vma, address, pmd); > + deferred_split_folio(folio, false); > + spin_unlock(pmd_ptl); > + } else { //mTHP > + mthp_pte = mk_pte(&folio->page, vma->vm_page_prot); > + mthp_pte = maybe_mkwrite(pte_mkdirty(mthp_pte), vma); > + > + spin_lock(pmd_ptl); > + folio_ref_add(folio, (1 << order) - 1); > + folio_add_new_anon_rmap(folio, vma, _address, RMAP_EXCLUSIVE); > + folio_add_lru_vma(folio, vma); > + spin_lock(pte_ptl); > + set_ptes(vma->vm_mm, _address, pte, mthp_pte, (1 << order)); > + update_mmu_cache_range(NULL, vma, _address, pte, (1 << order)); > + spin_unlock(pte_ptl); > + smp_wmb(); /* make pte visible before pmd */ > + pmd_populate(mm, pmd, pmd_pgtable(_pmd)); > + deferred_split_folio(folio, false); > + spin_unlock(pmd_ptl); > + } > > folio = NULL; > > @@ -1353,21 +1374,27 @@ static int khugepaged_scan_pmd(struct mm_struct *mm, > { > pmd_t *pmd; > pte_t *pte, *_pte; > + int i; > int result = SCAN_FAIL, referenced = 0; > int none_or_zero = 0, shared = 0; > struct page *page = NULL; > struct folio *folio = NULL; > unsigned long _address; > + unsigned long enabled_orders; > spinlock_t *ptl; > int node = NUMA_NO_NODE, unmapped = 0; > bool writable = false; > - > + int chunk_none_count = 0; > + int scaled_none = khugepaged_max_ptes_none >> (HPAGE_PMD_ORDER - MIN_MTHP_ORDER); > + unsigned long tva_flags = cc->is_khugepaged ? TVA_ENFORCE_SYSFS : 0; > VM_BUG_ON(address & ~HPAGE_PMD_MASK); > > result = find_pmd_or_thp_or_none(mm, address, &pmd); > if (result != SCAN_SUCCEED) > goto out; > > + bitmap_zero(cc->mthp_bitmap, MAX_MTHP_BITMAP_SIZE); > + bitmap_zero(cc->mthp_bitmap_temp, MAX_MTHP_BITMAP_SIZE); > memset(cc->node_load, 0, sizeof(cc->node_load)); > nodes_clear(cc->alloc_nmask); > pte = pte_offset_map_lock(mm, pmd, address, &ptl); > @@ -1376,8 +1403,12 @@ static int khugepaged_scan_pmd(struct mm_struct *mm, > goto out; > } > > - for (_address = address, _pte = pte; _pte < pte + HPAGE_PMD_NR; > - _pte++, _address += PAGE_SIZE) { > + for (i = 0; i < HPAGE_PMD_NR; i++) { > + if (i % MIN_MTHP_NR == 0) > + chunk_none_count = 0; > + > + _pte = pte + i; > + _address = address + i * PAGE_SIZE; > pte_t pteval = ptep_get(_pte); > if (is_swap_pte(pteval)) { > ++unmapped; > @@ -1400,16 +1431,14 @@ static int khugepaged_scan_pmd(struct mm_struct *mm, > } > } > if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { > + ++chunk_none_count; > ++none_or_zero; > - if (!userfaultfd_armed(vma) && > - (!cc->is_khugepaged || > - none_or_zero <= khugepaged_max_ptes_none)) { > - continue; > - } else { > + if (userfaultfd_armed(vma)) { Its likely you might introduce a regression in khugepaged cpu usage over here. For intel x86 machines that dont have TLB coalescing (AMD) or contpte (ARM), there is a reduced benefit of mTHPs, I feel like a lot of people will never change from the current kernel default, i.e. 2M THPs and fallback to 4K. If you are only parsing 2M hugepages, early bailout when none_or_zero <= khugepaged_max_ptes_none is a good optimization, and getting rid of that will cause a regression? It might look a bit out of place, but is it possible to keep this restriction of max_ptes_none during the scanning phase if only PMD mappable THPs are allowed? > result = SCAN_EXCEED_NONE_PTE; > count_vm_event(THP_SCAN_EXCEED_NONE_PTE); > goto out_unmap; > } > + continue; > } > if (pte_uffd_wp(pteval)) { > /* > @@ -1500,7 +1529,16 @@ static int khugepaged_scan_pmd(struct mm_struct *mm, > folio_test_referenced(folio) || mmu_notifier_test_young(vma->vm_mm, > address))) > referenced++; > + > + /* > + * we are reading in MIN_MTHP_NR page chunks. if there are no empty > + * pages keep track of it in the bitmap for mTHP collapsing. > + */ > + if (chunk_none_count < scaled_none && > + (i + 1) % MIN_MTHP_NR == 0) > + bitmap_set(cc->mthp_bitmap, i / MIN_MTHP_NR, 1); > } > + > if (!writable) { > result = SCAN_PAGE_RO; > } else if (cc->is_khugepaged && > @@ -1513,10 +1551,14 @@ static int khugepaged_scan_pmd(struct mm_struct *mm, > out_unmap: > pte_unmap_unlock(pte, ptl); > if (result == SCAN_SUCCEED) { > - result = collapse_huge_page(mm, address, referenced, > - unmapped, cc, mmap_locked, HPAGE_PMD_ORDER, 0); > - /* collapse_huge_page will return with the mmap_lock released */ > - *mmap_locked = false; > + enabled_orders = thp_vma_allowable_orders(vma, vma->vm_flags, > + tva_flags, THP_ORDERS_ALL_ANON); > + result = khugepaged_scan_bitmap(mm, address, referenced, unmapped, cc, > + mmap_locked, enabled_orders); > + if (result > 0) > + result = SCAN_SUCCEED; > + else > + result = SCAN_FAIL; > } > out: > trace_mm_khugepaged_scan_pmd(mm, &folio->page, writable, referenced, > @@ -2476,11 +2518,13 @@ static int khugepaged_collapse_single_pmd(unsigned long addr, struct mm_struct * > fput(file); > if (result == SCAN_PTE_MAPPED_HUGEPAGE) { > mmap_read_lock(mm); > + *mmap_locked = true; > if (khugepaged_test_exit_or_disable(mm)) > goto end; > result = collapse_pte_mapped_thp(mm, addr, > !cc->is_khugepaged); > mmap_read_unlock(mm); > + *mmap_locked = false; > } > } else { > result = khugepaged_scan_pmd(mm, vma, addr,