From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> Subject: khugepaged: allow to collapse PTE-mapped compound pages 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. Link: http://lkml.kernel.org/r/20200416160026.16538-7-kirill.shutemov@xxxxxxxxxxxxxxx Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Reviewed-by: William Kucharski <william.kucharski@xxxxxxxxxx> Reviewed-by: Zi Yan <ziy@xxxxxxxxxx> Tested-by: Zi Yan <ziy@xxxxxxxxxx> Acked-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: John Hubbard <jhubbard@xxxxxxxxxx> Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Cc: Ralph Campbell <rcampbell@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/khugepaged.c | 99 ++++++++++++++++++++++++++++++---------------- 1 file changed, 65 insertions(+), 34 deletions(-) --- a/mm/khugepaged.c~khugepaged-allow-to-collapse-pte-mapped-compound-pages +++ a/mm/khugepaged.c @@ -512,17 +512,30 @@ void __khugepaged_exit(struct mm_struct static void release_pte_page(struct page *page) { - dec_node_page_state(page, NR_ISOLATED_ANON + page_is_file_lru(page)); + mod_node_page_state(page_pgdat(page), + NR_ISOLATED_ANON + page_is_file_lru(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); } } @@ -539,7 +552,8 @@ static bool is_refcount_suitable(struct 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; @@ -569,13 +583,21 @@ static int __collapse_huge_page_isolate( 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 @@ -604,19 +626,15 @@ static int __collapse_huge_page_isolate( 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; } /* @@ -628,16 +646,23 @@ static int __collapse_huge_page_isolate( result = SCAN_DEL_PAGE_LRU; goto out; } - inc_node_page_state(page, - NR_ISOLATED_ANON + page_is_file_lru(page)); + mod_node_page_state(page_pgdat(page), + NR_ISOLATED_ANON + page_is_file_lru(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)) { @@ -651,7 +676,7 @@ static int __collapse_huge_page_isolate( } 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; @@ -660,13 +685,14 @@ out: 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); @@ -686,7 +712,8 @@ static void __collapse_huge_page_copy(pt } else { src_page = pte_page(pteval); copy_user_highpage(page, src_page, address, vma); - release_pte_page(src_page); + if (!PageCompound(src_page)) + release_pte_page(src_page); /* * ptl mostly unnecessary, but preempt has to * be disabled to update the per-cpu stats @@ -703,6 +730,11 @@ static void __collapse_huge_page_copy(pt 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); + } } static void khugepaged_alloc_sleep(void) @@ -961,6 +993,7 @@ static void collapse_huge_page(struct mm struct page **hpage, int node, int referenced, int unmapped) { + LIST_HEAD(compound_pagelist); pmd_t *pmd, _pmd; pte_t *pte; pgtable_t pgtable; @@ -1061,7 +1094,8 @@ static void collapse_huge_page(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)) { @@ -1086,7 +1120,8 @@ static void collapse_huge_page(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); @@ -1205,11 +1240,7 @@ static int khugepaged_scan_pmd(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 _
