[PATCH] ksm: set anon_vma of first rmap_item of ksm page to page's anon_vma other than vma's anon_vma

[zhouxianrong]

From: z00281421 <z00281...@notesmail.huawei.com>

set anon_vma of first rmap_item of ksm page to page's anon_vma
other than vma's anon_vma so that we can lookup all the forked
vma of kpage via reserve map. thus we can try_to_unmap ksm page
completely and reclaim or migrate the ksm page successfully and
need not to merg other forked vma addresses of ksm page with
building a rmap_item for it ever after.

a forked more mapcount ksm page with partially merged vma addresses and
a ksm page mapped into non-VM_MERGEABLE vma due to setting MADV_MERGEABLE
on one of the forked vma can be unmapped completely by try_to_unmap.

Signed-off-by: z00281421 <z00281...@notesmail.huawei.com>
---
 mm/ksm.c |   19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/mm/ksm.c b/mm/ksm.c
index 4786b41..6bacc08 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -971,11 +971,13 @@ out:
  * @page: the PageAnon page that we want to replace with kpage
  * @kpage: the PageKsm page that we want to map instead of page,
  *         or NULL the first time when we want to use page as kpage.
+ * @anon_vma: output the anon_vma of page used as kpage
  *
  * This function returns 0 if the pages were merged, -EFAULT otherwise.
  */
 static int try_to_merge_one_page(struct vm_area_struct *vma,
-                                struct page *page, struct page *kpage)
+                                struct page *page, struct page *kpage,
+                                struct anon_vma **anon_vma)
 {
        pte_t orig_pte = __pte(0);
        int err = -EFAULT;
@@ -1015,6 +1017,8 @@ static int try_to_merge_one_page(struct vm_area_struct 
*vma,
                         * PageAnon+anon_vma to PageKsm+NULL stable_node:
                         * stable_tree_insert() will update stable_node.
                         */
+                       if (anon_vma != NULL)
+                               *anon_vma = page_anon_vma(page);
                        set_page_stable_node(page, NULL);
                        mark_page_accessed(page);
                        /*
@@ -1055,6 +1059,7 @@ static int try_to_merge_with_ksm_page(struct rmap_item 
*rmap_item,
 {
        struct mm_struct *mm = rmap_item->mm;
        struct vm_area_struct *vma;
+       struct anon_vma *anon_vma = NULL;
        int err = -EFAULT;
 
        down_read(&mm->mmap_sem);
@@ -1062,7 +1067,7 @@ static int try_to_merge_with_ksm_page(struct rmap_item 
*rmap_item,
        if (!vma)
                goto out;
 
-       err = try_to_merge_one_page(vma, page, kpage);
+       err = try_to_merge_one_page(vma, page, kpage, &anon_vma);
        if (err)
                goto out;
 
@@ -1070,7 +1075,10 @@ static int try_to_merge_with_ksm_page(struct rmap_item 
*rmap_item,
        remove_rmap_item_from_tree(rmap_item);
 
        /* Must get reference to anon_vma while still holding mmap_sem */
-       rmap_item->anon_vma = vma->anon_vma;
+       if (anon_vma != NULL)
+               rmap_item->anon_vma = anon_vma;
+       else
+               rmap_item->anon_vma = vma->anon_vma;
        get_anon_vma(vma->anon_vma);
 out:
        up_read(&mm->mmap_sem);
@@ -1435,6 +1443,11 @@ static void cmp_and_merge_page(struct page *page, struct 
rmap_item *rmap_item)
 
        remove_rmap_item_from_tree(rmap_item);
 
+       if (kpage == page) {
+               put_page(kpage);
+               return;
+       }
+
        if (kpage) {
                err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
                if (!err) {
-- 
1.7.9.5