From ca0984caa8235762dc4e22c1c47ae6719dcc4064 Mon Sep 17 00:00:00 2001 From: Ebru Akagunduz Date: Tue, 14 Apr 2015 15:45:24 -0700 Subject: [PATCH] mm: incorporate zero pages into transparent huge pages This patch improves THP collapse rates, by allowing zero pages. Currently THP can collapse 4kB pages into a THP when there are up to khugepaged_max_ptes_none pte_none ptes in a 2MB range. This patch counts pte none and mapped zero pages with the same variable. The patch was tested with a program that allocates 800MB of memory, and performs interleaved reads and writes, in a pattern that causes some 2MB areas to first see read accesses, resulting in the zero pfn being mapped there. To simulate memory fragmentation at allocation time, I modified do_huge_pmd_anonymous_page to return VM_FAULT_FALLBACK for read faults. Without the patch, only %50 of the program was collapsed into THP and the percentage did not increase over time. With this patch after 10 minutes of waiting khugepaged had collapsed %99 of the program's memory. [aarcange@redhat.com: fix bogus BUG()] Signed-off-by: Ebru Akagunduz Reviewed-by: Rik van Riel Reviewed-by: Andrea Arcangeli Acked-by: Kirill A. Shutemov Acked-by: Vlastimil Babka Cc: Hugh Dickins Cc: Johannes Weiner Cc: Sasha Levin Cc: David Rientjes Cc: Mel Gorman Signed-off-by: Andrea Arcangeli Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/huge_memory.c | 28 ++++++++++++++++++++-------- 1 file changed, 20 insertions(+), 8 deletions(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 10a4b6cea0d1..6352c1dfa898 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2109,7 +2109,7 @@ static void release_pte_pages(pte_t *pte, pte_t *_pte) { while (--_pte >= pte) { pte_t pteval = *_pte; - if (!pte_none(pteval)) + if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval))) release_pte_page(pte_page(pteval)); } } @@ -2120,13 +2120,13 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma, { struct page *page; pte_t *_pte; - int none = 0; + int none_or_zero = 0; bool referenced = false, writable = false; for (_pte = pte; _pte < pte+HPAGE_PMD_NR; _pte++, address += PAGE_SIZE) { pte_t pteval = *_pte; - if (pte_none(pteval)) { - if (++none <= khugepaged_max_ptes_none) + if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { + if (++none_or_zero <= khugepaged_max_ptes_none) continue; else goto out; @@ -2207,9 +2207,21 @@ static void __collapse_huge_page_copy(pte_t *pte, struct page *page, pte_t pteval = *_pte; struct page *src_page; - if (pte_none(pteval)) { + if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { clear_user_highpage(page, address); add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1); + if (is_zero_pfn(pte_pfn(pteval))) { + /* + * ptl mostly unnecessary. + */ + spin_lock(ptl); + /* + * paravirt calls inside pte_clear here are + * superfluous. + */ + pte_clear(vma->vm_mm, address, _pte); + spin_unlock(ptl); + } } else { src_page = pte_page(pteval); copy_user_highpage(page, src_page, address, vma); @@ -2543,7 +2555,7 @@ static int khugepaged_scan_pmd(struct mm_struct *mm, { pmd_t *pmd; pte_t *pte, *_pte; - int ret = 0, none = 0; + int ret = 0, none_or_zero = 0; struct page *page; unsigned long _address; spinlock_t *ptl; @@ -2561,8 +2573,8 @@ static int khugepaged_scan_pmd(struct mm_struct *mm, for (_address = address, _pte = pte; _pte < pte+HPAGE_PMD_NR; _pte++, _address += PAGE_SIZE) { pte_t pteval = *_pte; - if (pte_none(pteval)) { - if (++none <= khugepaged_max_ptes_none) + if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { + if (++none_or_zero <= khugepaged_max_ptes_none) continue; else goto out_unmap;