Messages in this thread | | | Subject | Re: [PATCHv2 6/8] khugepaged: Allow to collapse PTE-mapped compound pages | From | Yang Shi <> | Date | Mon, 6 Apr 2020 14:29:35 -0700 |
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On 4/3/20 4:29 AM, Kirill A. Shutemov wrote: > We can collapse PTE-mapped compound pages. We only need to avoid > handling them more than once: lock/unlock page only once if it's present > in the PMD range multiple times as it handled on compound level. The > same goes for LRU isolation and putback. > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > --- > mm/khugepaged.c | 103 ++++++++++++++++++++++++++++++++---------------- > 1 file changed, 68 insertions(+), 35 deletions(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 1e7e6543ebca..49e56e4e30d1 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -515,23 +515,37 @@ void __khugepaged_exit(struct mm_struct *mm) > > static void release_pte_page(struct page *page) > { > - dec_node_page_state(page, NR_ISOLATED_ANON + page_is_file_cache(page)); > + mod_node_page_state(page_pgdat(page), > + NR_ISOLATED_ANON + page_is_file_cache(page), > + -compound_nr(page)); > unlock_page(page); > putback_lru_page(page); > } > > -static void release_pte_pages(pte_t *pte, pte_t *_pte) > +static void release_pte_pages(pte_t *pte, pte_t *_pte, > + struct list_head *compound_pagelist) > { > + struct page *page, *tmp; > + > while (--_pte >= pte) { > pte_t pteval = *_pte; > - if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval))) > - release_pte_page(pte_page(pteval)); > + > + page = pte_page(pteval); > + if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval)) && > + !PageCompound(page)) > + release_pte_page(page); > + } > + > + list_for_each_entry_safe(page, tmp, compound_pagelist, lru) { > + list_del(&page->lru); > + release_pte_page(page); > } > } > > static int __collapse_huge_page_isolate(struct vm_area_struct *vma, > unsigned long address, > - pte_t *pte) > + pte_t *pte, > + struct list_head *compound_pagelist) > { > struct page *page = NULL; > pte_t *_pte; > @@ -561,13 +575,21 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma, > goto out; > } > > - /* TODO: teach khugepaged to collapse THP mapped with pte */ > + VM_BUG_ON_PAGE(!PageAnon(page), page); > + > if (PageCompound(page)) { > - result = SCAN_PAGE_COMPOUND; > - goto out; > - } > + struct page *p; > + page = compound_head(page); > > - VM_BUG_ON_PAGE(!PageAnon(page), page); > + /* > + * Check if we have dealt with the compound page > + * already > + */ > + list_for_each_entry(p, compound_pagelist, lru) { > + if (page == p) > + goto next; > + } > + } > > /* > * We can do it before isolate_lru_page because the > @@ -597,19 +619,15 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma, > result = SCAN_PAGE_COUNT; > goto out; > } > - if (pte_write(pteval)) { > - writable = true; > - } else { > - if (PageSwapCache(page) && > - !reuse_swap_page(page, NULL)) { > - unlock_page(page); > - result = SCAN_SWAP_CACHE_PAGE; > - goto out; > - } > + if (!pte_write(pteval) && PageSwapCache(page) && > + !reuse_swap_page(page, NULL)) { > /* > - * Page is not in the swap cache. It can be collapsed > - * into a THP. > + * Page is in the swap cache and cannot be re-used. > + * It cannot be collapsed into a THP. > */ > + unlock_page(page); > + result = SCAN_SWAP_CACHE_PAGE; > + goto out; > } > > /* > @@ -621,16 +639,23 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma, > result = SCAN_DEL_PAGE_LRU; > goto out; > } > - inc_node_page_state(page, > - NR_ISOLATED_ANON + page_is_file_cache(page)); > + mod_node_page_state(page_pgdat(page), > + NR_ISOLATED_ANON + page_is_file_cache(page), > + compound_nr(page)); > VM_BUG_ON_PAGE(!PageLocked(page), page); > VM_BUG_ON_PAGE(PageLRU(page), page); > > + if (PageCompound(page)) > + list_add_tail(&page->lru, compound_pagelist); > +next: > /* There should be enough young pte to collapse the page */ > if (pte_young(pteval) || > page_is_young(page) || PageReferenced(page) || > mmu_notifier_test_young(vma->vm_mm, address)) > referenced++; > + > + if (pte_write(pteval)) > + writable = true; > } > if (likely(writable)) { > if (likely(referenced)) { > @@ -644,7 +669,7 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma, > } > > out: > - release_pte_pages(pte, _pte); > + release_pte_pages(pte, _pte, compound_pagelist); > trace_mm_collapse_huge_page_isolate(page, none_or_zero, > referenced, writable, result); > return 0; > @@ -653,13 +678,14 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma, > static void __collapse_huge_page_copy(pte_t *pte, struct page *page, > struct vm_area_struct *vma, > unsigned long address, > - spinlock_t *ptl) > + spinlock_t *ptl, > + struct list_head *compound_pagelist) > { > + struct page *src_page, *tmp; > pte_t *_pte; > for (_pte = pte; _pte < pte + HPAGE_PMD_NR; > _pte++, page++, address += PAGE_SIZE) { > pte_t pteval = *_pte; > - struct page *src_page; > > if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { > clear_user_highpage(page, address); > @@ -679,7 +705,6 @@ static void __collapse_huge_page_copy(pte_t *pte, struct page *page, > } else { > src_page = pte_page(pteval); > copy_user_highpage(page, src_page, address, vma); > - release_pte_page(src_page); > /* > * ptl mostly unnecessary, but preempt has to > * be disabled to update the per-cpu stats > @@ -693,9 +718,18 @@ static void __collapse_huge_page_copy(pte_t *pte, struct page *page, > pte_clear(vma->vm_mm, address, _pte); > page_remove_rmap(src_page, false); > spin_unlock(ptl); > - free_page_and_swap_cache(src_page); > + if (!PageCompound(src_page)) { > + release_pte_page(src_page); > + free_page_and_swap_cache(src_page); > + } > } > } > + > + list_for_each_entry_safe(src_page, tmp, compound_pagelist, lru) { > + list_del(&src_page->lru); > + release_pte_page(src_page); > + free_page_and_swap_cache(src_page); > + }
It looks this may mess up the PTE-mapped THP's refcount if it has multiple PTE-mapped subpages since put_page() is not called for every PTE-mapped subpages.
> } > > static void khugepaged_alloc_sleep(void) > @@ -960,6 +994,7 @@ static void collapse_huge_page(struct mm_struct *mm, > struct page **hpage, > int node, int referenced) > { > + LIST_HEAD(compound_pagelist); > pmd_t *pmd, _pmd; > pte_t *pte; > pgtable_t pgtable; > @@ -1059,7 +1094,8 @@ static void collapse_huge_page(struct mm_struct *mm, > mmu_notifier_invalidate_range_end(&range); > > spin_lock(pte_ptl); > - isolated = __collapse_huge_page_isolate(vma, address, pte); > + isolated = __collapse_huge_page_isolate(vma, address, pte, > + &compound_pagelist); > spin_unlock(pte_ptl); > > if (unlikely(!isolated)) { > @@ -1084,7 +1120,8 @@ static void collapse_huge_page(struct mm_struct *mm, > */ > anon_vma_unlock_write(vma->anon_vma); > > - __collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl); > + __collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl, > + &compound_pagelist); > pte_unmap(pte); > __SetPageUptodate(new_page); > pgtable = pmd_pgtable(_pmd); > @@ -1181,11 +1218,7 @@ static int khugepaged_scan_pmd(struct mm_struct *mm, > goto out_unmap; > } > > - /* TODO: teach khugepaged to collapse THP mapped with pte */ > - if (PageCompound(page)) { > - result = SCAN_PAGE_COMPOUND; > - goto out_unmap; > - } > + page = compound_head(page); > > /* > * Record which node the original page is from and save this
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