Messages in this thread | | | Date | Tue, 19 Jul 2022 15:49:49 +0530 | Subject | Re: [RFC PATCH 15/26] hugetlb: make unmapping compatible with high-granularity mappings | From | "manish.mishra" <> |
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On 24/06/22 11:06 pm, James Houghton wrote: > This enlightens __unmap_hugepage_range to deal with high-granularity > mappings. This doesn't change its API; it still must be called with > hugepage alignment, but it will correctly unmap hugepages that have been > mapped at high granularity. > > Analogous to the mapcount rules introduced by hugetlb_no_page, we only > drop mapcount in this case if we are unmapping an entire hugepage in one > operation. This is the case when a VMA is destroyed. > > Eventually, functionality here can be expanded to allow users to call > MADV_DONTNEED on PAGE_SIZE-aligned sections of a hugepage, but that is > not done here.
Sorry i may have misunderstood something here, but allowing something like
MADV_DONTNEED on PAGE_SIZE in hugetlbfs can cause fragmentation
in hugetlbfs pool which kind of looks opposite of prupose of hugetlbfs?
> > Signed-off-by: James Houghton <jthoughton@google.com> > --- > include/asm-generic/tlb.h | 6 +-- > mm/hugetlb.c | 85 ++++++++++++++++++++++++++------------- > 2 files changed, 59 insertions(+), 32 deletions(-) > > diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h > index ff3e82553a76..8daa3ae460d9 100644 > --- a/include/asm-generic/tlb.h > +++ b/include/asm-generic/tlb.h > @@ -562,9 +562,9 @@ static inline void tlb_flush_p4d_range(struct mmu_gather *tlb, > __tlb_remove_tlb_entry(tlb, ptep, address); \ > } while (0) > > -#define tlb_remove_huge_tlb_entry(h, tlb, ptep, address) \ > +#define tlb_remove_huge_tlb_entry(tlb, hpte, address) \ > do { \ > - unsigned long _sz = huge_page_size(h); \ > + unsigned long _sz = hugetlb_pte_size(&hpte); \ > if (_sz >= P4D_SIZE) \ > tlb_flush_p4d_range(tlb, address, _sz); \ > else if (_sz >= PUD_SIZE) \ > @@ -573,7 +573,7 @@ static inline void tlb_flush_p4d_range(struct mmu_gather *tlb, > tlb_flush_pmd_range(tlb, address, _sz); \ > else \ > tlb_flush_pte_range(tlb, address, _sz); \ > - __tlb_remove_tlb_entry(tlb, ptep, address); \ > + __tlb_remove_tlb_entry(tlb, hpte.ptep, address);\ > } while (0) > > /** > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index da30621656b8..51fc1d3f122f 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -5120,24 +5120,20 @@ static void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct > { > struct mm_struct *mm = vma->vm_mm; > unsigned long address; > - pte_t *ptep; > + struct hugetlb_pte hpte; > pte_t pte; > spinlock_t *ptl; > - struct page *page; > + struct page *hpage, *subpage; > struct hstate *h = hstate_vma(vma); > unsigned long sz = huge_page_size(h); > struct mmu_notifier_range range; > bool force_flush = false; > + bool hgm_enabled = hugetlb_hgm_enabled(vma); > > WARN_ON(!is_vm_hugetlb_page(vma)); > BUG_ON(start & ~huge_page_mask(h)); > BUG_ON(end & ~huge_page_mask(h)); > > - /* > - * This is a hugetlb vma, all the pte entries should point > - * to huge page. > - */ > - tlb_change_page_size(tlb, sz); > tlb_start_vma(tlb, vma); > > /* > @@ -5148,25 +5144,43 @@ static void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct > adjust_range_if_pmd_sharing_possible(vma, &range.start, &range.end); > mmu_notifier_invalidate_range_start(&range); > address = start; > - for (; address < end; address += sz) { > - ptep = huge_pte_offset(mm, address, sz); > - if (!ptep) > + > + while (address < end) { > + pte_t *ptep = huge_pte_offset(mm, address, sz); > + > + if (!ptep) { > + address += sz; > continue; > + } > + hugetlb_pte_populate(&hpte, ptep, huge_page_shift(h)); > + if (hgm_enabled) { > + int ret = huge_pte_alloc_high_granularity( > + &hpte, mm, vma, address, PAGE_SHIFT, > + HUGETLB_SPLIT_NEVER, > + /*write_locked=*/true);
I see huge_pte_alloc_high_granularity with HUGETLB_SPLIT_NEVER just
do huge_tlb_walk. So is HUGETLB_SPLIT_NEVER even required, i mean
for those cases you can directly do huge_tlb_walk? I mean name
huge_pte_alloc_high_granularity confuses for those cases.
> + /* > + * We will never split anything, so this should always > + * succeed. > + */ > + BUG_ON(ret); > + } > > - ptl = huge_pte_lock(h, mm, ptep); > - if (huge_pmd_unshare(mm, vma, &address, ptep)) { > + ptl = hugetlb_pte_lock(mm, &hpte); > + if (!hgm_enabled && huge_pmd_unshare( > + mm, vma, &address, hpte.ptep)) { > spin_unlock(ptl); > tlb_flush_pmd_range(tlb, address & PUD_MASK, PUD_SIZE); > force_flush = true; > - continue; > + goto next_hpte; > } > > - pte = huge_ptep_get(ptep); > - if (huge_pte_none(pte)) { > + if (hugetlb_pte_none(&hpte)) { > spin_unlock(ptl); > - continue; > + goto next_hpte; > } > > + pte = hugetlb_ptep_get(&hpte); > + > /* > * Migrating hugepage or HWPoisoned hugepage is already > * unmapped and its refcount is dropped, so just clear pte here. > @@ -5180,24 +5194,27 @@ static void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct > */ > if (pte_swp_uffd_wp_any(pte) && > !(zap_flags & ZAP_FLAG_DROP_MARKER)) > - set_huge_pte_at(mm, address, ptep, > + set_huge_pte_at(mm, address, hpte.ptep, > make_pte_marker(PTE_MARKER_UFFD_WP)); > else > - huge_pte_clear(mm, address, ptep, sz); > + huge_pte_clear(mm, address, hpte.ptep, > + hugetlb_pte_size(&hpte)); > spin_unlock(ptl); > - continue; > + goto next_hpte; > } > > - page = pte_page(pte); > + subpage = pte_page(pte); > + BUG_ON(!subpage); > + hpage = compound_head(subpage); > /* > * If a reference page is supplied, it is because a specific > * page is being unmapped, not a range. Ensure the page we > * are about to unmap is the actual page of interest. > */ > if (ref_page) { > - if (page != ref_page) { > + if (hpage != ref_page) { > spin_unlock(ptl); > - continue; > + goto next_hpte; > } > /* > * Mark the VMA as having unmapped its page so that > @@ -5207,25 +5224,35 @@ static void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct > set_vma_resv_flags(vma, HPAGE_RESV_UNMAPPED); > } > > - pte = huge_ptep_get_and_clear(mm, address, ptep); > - tlb_remove_huge_tlb_entry(h, tlb, ptep, address); > + pte = huge_ptep_get_and_clear(mm, address, hpte.ptep); > + tlb_change_page_size(tlb, hugetlb_pte_size(&hpte)); > + tlb_remove_huge_tlb_entry(tlb, hpte, address); > if (huge_pte_dirty(pte)) > - set_page_dirty(page); > + set_page_dirty(hpage); > /* Leave a uffd-wp pte marker if needed */ > if (huge_pte_uffd_wp(pte) && > !(zap_flags & ZAP_FLAG_DROP_MARKER)) > - set_huge_pte_at(mm, address, ptep, > + set_huge_pte_at(mm, address, hpte.ptep, > make_pte_marker(PTE_MARKER_UFFD_WP)); > - hugetlb_count_sub(pages_per_huge_page(h), mm); > - page_remove_rmap(page, vma, true); > + > + hugetlb_count_sub(hugetlb_pte_size(&hpte)/PAGE_SIZE, mm); > + > + /* > + * If we are unmapping the entire page, remove it from the > + * rmap. > + */ > + if (IS_ALIGNED(address, sz) && address + sz <= end) > + page_remove_rmap(hpage, vma, true); > > spin_unlock(ptl); > - tlb_remove_page_size(tlb, page, huge_page_size(h)); > + tlb_remove_page_size(tlb, subpage, hugetlb_pte_size(&hpte)); > /* > * Bail out after unmapping reference page if supplied > */ > if (ref_page) > break; > +next_hpte: > + address += hugetlb_pte_size(&hpte); > } > mmu_notifier_invalidate_range_end(&range); > tlb_end_vma(tlb, vma);
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