[RFC PATCH v2 05/19] mm: support disabling of ksm for a process

[Stefan Roesch <shr@devkernel.io>]

This adds the ability to disable ksm for a process if ksm has been
enabled for the process.

Signed-off-by: Stefan Roesch <shr@devkernel.io>
---
 mm/ksm.c | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/mm/ksm.c b/mm/ksm.c
index efd8d3804de3..23d6944f78ad 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -2690,6 +2690,27 @@ int __ksm_enter(struct mm_struct *mm, int flag)
 	return 0;
 }
 
+static void unmerge_vmas(struct mm_struct *mm)
+{
+	struct vm_area_struct *vma;
+	struct vma_iterator vmi;
+
+	vma_iter_init(&vmi, mm, 0);
+
+	mmap_read_lock(mm);
+	for_each_vma(vmi, vma) {
+		if (vma->vm_flags & VM_MERGEABLE) {
+			unsigned long flags = vma->vm_flags;
+
+			if (ksm_madvise(vma, vma->vm_start, vma->vm_end, MADV_UNMERGEABLE, &flags))
+				continue;
+
+			vm_flags_clear(vma, VM_MERGEABLE);
+		}
+	}
+	mmap_read_unlock(mm);
+}
+
 void __ksm_exit(struct mm_struct *mm, int flag)
 {
 	struct ksm_mm_slot *mm_slot;
@@ -2697,8 +2718,10 @@ void __ksm_exit(struct mm_struct *mm, int flag)
 	int easy_to_free = 0;
 
 	if (!(current->flags & PF_EXITING) && flag == MMF_VM_MERGE_ANY &&
-	    test_bit(MMF_VM_MERGE_ANY, &mm->flags))
+		test_bit(MMF_VM_MERGE_ANY, &mm->flags)) {
 		clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
+		unmerge_vmas(mm);
+	}
 
 	/*
 	 * This process is exiting: if it's straightforward (as is the
-- 
2.30.2