From 8eaedede825a02dbe2420b9c9be9b5b2d7515496 Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" Date: Fri, 24 Feb 2017 14:57:48 -0800 Subject: [PATCH] mm: fix handling PTE-mapped THPs in page_referenced() For PTE-mapped THP page_check_address_transhuge() is not adequate: it cannot find all relevant PTEs, only the first one. It means we can miss some references of the page and it can result in suboptimal decisions by vmscan. Let's switch it to page_vma_mapped_walk(). I don't think it's subject for stable@: it's not fatal. The only side effect is that THP can be swapped out when it shouldn't. Link: http://lkml.kernel.org/r/20170129173858.45174-4-kirill.shutemov@linux.intel.com Signed-off-by: Kirill A. Shutemov Cc: Andrea Arcangeli Cc: Hillf Danton Cc: Hugh Dickins Cc: Johannes Weiner Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Rik van Riel Cc: Srikar Dronamraju Cc: Vladimir Davydov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/rmap.c | 66 ++++++++++++++++++++++++++++--------------------------- 1 file changed, 34 insertions(+), 32 deletions(-) diff --git a/mm/rmap.c b/mm/rmap.c index 91619fd70939..0dff8accd629 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -886,45 +886,48 @@ struct page_referenced_arg { static int page_referenced_one(struct page *page, struct vm_area_struct *vma, unsigned long address, void *arg) { - struct mm_struct *mm = vma->vm_mm; struct page_referenced_arg *pra = arg; - pmd_t *pmd; - pte_t *pte; - spinlock_t *ptl; + struct page_vma_mapped_walk pvmw = { + .page = page, + .vma = vma, + .address = address, + }; int referenced = 0; - if (!page_check_address_transhuge(page, mm, address, &pmd, &pte, &ptl)) - return SWAP_AGAIN; + while (page_vma_mapped_walk(&pvmw)) { + address = pvmw.address; - if (vma->vm_flags & VM_LOCKED) { - if (pte) - pte_unmap(pte); - spin_unlock(ptl); - pra->vm_flags |= VM_LOCKED; - return SWAP_FAIL; /* To break the loop */ - } + if (vma->vm_flags & VM_LOCKED) { + page_vma_mapped_walk_done(&pvmw); + pra->vm_flags |= VM_LOCKED; + return SWAP_FAIL; /* To break the loop */ + } - if (pte) { - if (ptep_clear_flush_young_notify(vma, address, pte)) { - /* - * Don't treat a reference through a sequentially read - * mapping as such. If the page has been used in - * another mapping, we will catch it; if this other - * mapping is already gone, the unmap path will have - * set PG_referenced or activated the page. - */ - if (likely(!(vma->vm_flags & VM_SEQ_READ))) + if (pvmw.pte) { + if (ptep_clear_flush_young_notify(vma, address, + pvmw.pte)) { + /* + * Don't treat a reference through + * a sequentially read mapping as such. + * If the page has been used in another mapping, + * we will catch it; if this other mapping is + * already gone, the unmap path will have set + * PG_referenced or activated the page. + */ + if (likely(!(vma->vm_flags & VM_SEQ_READ))) + referenced++; + } + } else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) { + if (pmdp_clear_flush_young_notify(vma, address, + pvmw.pmd)) referenced++; + } else { + /* unexpected pmd-mapped page? */ + WARN_ON_ONCE(1); } - pte_unmap(pte); - } else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) { - if (pmdp_clear_flush_young_notify(vma, address, pmd)) - referenced++; - } else { - /* unexpected pmd-mapped page? */ - WARN_ON_ONCE(1); + + pra->mapcount--; } - spin_unlock(ptl); if (referenced) clear_page_idle(page); @@ -936,7 +939,6 @@ static int page_referenced_one(struct page *page, struct vm_area_struct *vma, pra->vm_flags |= vma->vm_flags; } - pra->mapcount--; if (!pra->mapcount) return SWAP_SUCCESS; /* To break the loop */ -- 2.20.1