[RFC PATCH v2 04/19] mm: invoke madvise for all vmas in scan_get_next_rmap_item

[Stefan Roesch <shr@devkernel.io>]

If the new flag MMF_VM_MERGE_ANY has been set for a process, iterate
over all the vmas and enable ksm if possible. For the vmas that can be
ksm enabled this is only done once.

Signed-off-by: Stefan Roesch <shr@devkernel.io>
---
 mm/ksm.c | 27 ++++++++++++++++++++++++++-
 1 file changed, 26 insertions(+), 1 deletion(-)

diff --git a/mm/ksm.c b/mm/ksm.c
index 3597ae52fe7b..efd8d3804de3 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -1063,6 +1063,7 @@ static int unmerge_and_remove_all_rmap_items(void)
 
 			mm_slot_free(mm_slot_cache, mm_slot);
 			clear_bit(MMF_VM_MERGEABLE, &mm->flags);
+			clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
 			mmdrop(mm);
 		} else
 			spin_unlock(&ksm_mmlist_lock);
@@ -2329,6 +2330,17 @@ static struct ksm_rmap_item *get_next_rmap_item(struct ksm_mm_slot *mm_slot,
 	return rmap_item;
 }
 
+static bool vma_ksm_mergeable(struct vm_area_struct *vma)
+{
+	if (vma->vm_flags & VM_MERGEABLE)
+		return true;
+
+	if (test_bit(MMF_VM_MERGE_ANY, &vma->vm_mm->flags))
+		return true;
+
+	return false;
+}
+
 static struct ksm_rmap_item *scan_get_next_rmap_item(struct page **page)
 {
 	struct mm_struct *mm;
@@ -2405,8 +2417,20 @@ static struct ksm_rmap_item *scan_get_next_rmap_item(struct page **page)
 		goto no_vmas;
 
 	for_each_vma(vmi, vma) {
-		if (!(vma->vm_flags & VM_MERGEABLE))
+		if (!vma_ksm_mergeable(vma))
 			continue;
+		if (!(vma->vm_flags & VM_MERGEABLE)) {
+			unsigned long flags = vma->vm_flags;
+
+			/* madvise failed, use next vma */
+			if (ksm_madvise(vma, vma->vm_start, vma->vm_end, MADV_MERGEABLE, &flags))
+				continue;
+			/* vma, not supported as being mergeable */
+			if (!(flags & VM_MERGEABLE))
+				continue;
+
+			vm_flags_set(vma, VM_MERGEABLE);
+		}
 		if (ksm_scan.address < vma->vm_start)
 			ksm_scan.address = vma->vm_start;
 		if (!vma->anon_vma)
@@ -2491,6 +2515,7 @@ static struct ksm_rmap_item *scan_get_next_rmap_item(struct page **page)
 
 		mm_slot_free(mm_slot_cache, mm_slot);
 		clear_bit(MMF_VM_MERGEABLE, &mm->flags);
+		clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
 		mmap_read_unlock(mm);
 		mmdrop(mm);
 	} else {
-- 
2.30.2