Commit 3e321587 authored Dec 12, 2016 by Andi Kleen Committed by Linus Torvalds Dec 12, 2016

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 <ak@linux.intel.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent bf00bd34

mm/mprotect.c

+13 −0

Original line number	Diff line number	Diff line
		@@ -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);

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