| Message ID | 20250211003028.213461-8-npache@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | khugepaged: mTHP support | expand |
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 <npache@redhat.com> > --- > 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); Hi Nico, This patch will have the same issue as the one I pointed out in https://lore.kernel.org/all/82b9efd1-f2a6-4452-b2ea-6c163e17cdf7@gmail.com/ ?
On Wed, Feb 12, 2025 at 10:04 AM Usama Arif <usamaarif642@gmail.com> wrote: > > > > 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 <npache@redhat.com> > > --- > > 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); > > > Hi Nico, > > This patch will have the same issue as the one I pointed out in > https://lore.kernel.org/all/82b9efd1-f2a6-4452-b2ea-6c163e17cdf7@gmail.com/ ? Hi Usama, Yes thanks for pointing that out! I'll make sure to remove the deferred_split_folio call. >
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 <npache@redhat.com> > --- > 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,
On Mon, Feb 17, 2025 at 1:55 PM Usama Arif <usamaarif642@gmail.com> wrote: > > > > 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 <npache@redhat.com> > > --- > > 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? That seems like a reasonable request, I will try to implement that. Thanks! > > > > > 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, >
On 11/02/25 6:00 am, 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 <npache@redhat.com> > --- > 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)); As I have mentioned before, since you are isolating the PTE table in both cases, you need to do the mmu_notifier_* stuff for HPAGE_PMD_SIZE in any case. Check out patch 8 from my patchset. > 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); My personal opinion is that this if-else nesting looks really weird. This is why I separated out mTHP collapse into a separate function. > + 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)) { > 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,
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 <npache@redhat.com> > --- > 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); I've only stared at this briefly, but it feels like there might be some bugs: - Why are you taking the pmd ptl? and calling pmd_populate? Surely the pte table already exists and is attached to the pmd? So we are only need to update the pte entries here? Or perhaps the whole pmd was previously isolated? - I think some arches use a single PTL for all levels of the pgtable? So in this case it's probably not a good idea to nest the pmd and pte spin lock? - Given the pte PTL is dropped then reacquired, is there any way that the ptes could have changed under us? Is any revalidation required? Perhaps not if pte table was removed from the PMD. - I would have guessed the memory ordering you want from smp_wmb() would already be handled by the spin_unlock()? > + } > > 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)) { > 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,
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)) { 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,
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 <npache@redhat.com> --- mm/khugepaged.c | 122 ++++++++++++++++++++++++++++++++---------------- 1 file changed, 83 insertions(+), 39 deletions(-)