From 3e32158767b04db60b83f760e1722fd15a715d7a Mon Sep 17 00:00:00 2001 From: Andi Kleen Date: Mon, 12 Dec 2016 16:41:47 -0800 Subject: [PATCH] mm/mprotect.c: don't touch single threaded PTEs which are on the right node We had some problems with pages getting unmapped in single threaded affinitized processes. It was tracked down to NUMA scanning. In this case it doesn't make any sense to unmap pages if the process is single threaded and the page is already on the node the process is running on. Add a check for this case into the numa protection code, and skip unmapping if true. In theory the process could be migrated later, but we will eventually rescan and unmap and migrate then. In theory this could be made more fancy: remembering this state per process or even whole mm. However that would need extra tracking and be more complicated, and the simple check seems to work fine so far. [ak@linux.intel.com: v3: Minor updates from Mel. Change code layout] Link: http://lkml.kernel.org/r/1476382117-5440-1-git-send-email-andi@firstfloor.org Link: http://lkml.kernel.org/r/1476288949-20970-1-git-send-email-andi@firstfloor.org Signed-off-by: Andi Kleen Acked-by: Mel Gorman Cc: Peter Zijlstra Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/mprotect.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/mm/mprotect.c b/mm/mprotect.c index 11936526b08b..05a02b72c98d 100644 --- a/mm/mprotect.c +++ b/mm/mprotect.c @@ -69,11 +69,17 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd, pte_t *pte, oldpte; spinlock_t *ptl; unsigned long pages = 0; + int target_node = NUMA_NO_NODE; pte = lock_pte_protection(vma, pmd, addr, prot_numa, &ptl); if (!pte) return 0; + /* Get target node for single threaded private VMAs */ + if (prot_numa && !(vma->vm_flags & VM_SHARED) && + atomic_read(&vma->vm_mm->mm_users) == 1) + target_node = numa_node_id(); + arch_enter_lazy_mmu_mode(); do { oldpte = *pte; @@ -95,6 +101,13 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd, /* Avoid TLB flush if possible */ if (pte_protnone(oldpte)) continue; + + /* + * Don't mess with PTEs if page is already on the node + * a single-threaded process is running on. + */ + if (target_node == page_to_nid(page)) + continue; } ptent = ptep_modify_prot_start(mm, addr, pte); -- 2.20.1