rmap: extend try_to_unmap() to be usable by split_huge_page()

Add support for two ttu_flags:

  - TTU_SPLIT_HUGE_PMD would split PMD if it's there, before trying to
    unmap page;

  - TTU_RMAP_LOCKED indicates that caller holds relevant rmap lock;

Also, change rwc->done to !page_mapcount() instead of !page_mapped().
try_to_unmap() works on pte level, so we are really interested in the
mappedness of this small page rather than of the compound page it's a
part of.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 16 insertions, 8 deletions

diff --git a/mm/rmap.c b/mm/rmap.c
index 30b739ce0ffa..945933a01010 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1431,6 +1431,8 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
         if ((flags & TTU_MUNLOCK) && !(vma->vm_flags & VM_LOCKED))
                 goto out;
 
+        if (flags & TTU_SPLIT_HUGE_PMD)
+                split_huge_pmd_address(vma, address);
         pte = page_check_address(page, mm, address, &ptl, 0);
         if (!pte)
                 goto out;
@@ -1576,10 +1578,10 @@ static bool invalid_migration_vma(struct vm_area_struct *vma, void *arg)
         return is_vma_temporary_stack(vma);
 }
 
-static int page_not_mapped(struct page *page)
+static int page_mapcount_is_zero(struct page *page)
 {
-        return !page_mapped(page);
-};
+        return !page_mapcount(page);
+}
 
 /**
  * try_to_unmap - try to remove all page table mappings to a page
@@ -1606,12 +1608,10 @@ int try_to_unmap(struct page *page, enum ttu_flags flags)
         struct rmap_walk_control rwc = {
                 .rmap_one = try_to_unmap_one,
                 .arg = &rp,
-                .done = page_not_mapped,
+                .done = page_mapcount_is_zero,
                 .anon_lock = page_lock_anon_vma_read,
         };
 
-        VM_BUG_ON_PAGE(!PageHuge(page) && PageTransHuge(page), page);
-
         /*
          * During exec, a temporary VMA is setup and later moved.
          * The VMA is moved under the anon_vma lock but not the
@@ -1623,9 +1623,12 @@ int try_to_unmap(struct page *page, enum ttu_flags flags)
         if ((flags & TTU_MIGRATION) && !PageKsm(page) && PageAnon(page))
                 rwc.invalid_vma = invalid_migration_vma;
 
-        ret = rmap_walk(page, &rwc);
+        if (flags & TTU_RMAP_LOCKED)
+                ret = rmap_walk_locked(page, &rwc);
+        else
+                ret = rmap_walk(page, &rwc);
 
-        if (ret != SWAP_MLOCK && !page_mapped(page)) {
+        if (ret != SWAP_MLOCK && !page_mapcount(page)) {
                 ret = SWAP_SUCCESS;
                 if (rp.lazyfreed && !PageDirty(page))
                         ret = SWAP_LZFREE;
@@ -1633,6 +1636,11 @@ int try_to_unmap(struct page *page, enum ttu_flags flags)
         return ret;
 }
 
+static int page_not_mapped(struct page *page)
+{
+        return !page_mapped(page);
+};
+
 /**
  * try_to_munlock - try to munlock a page
  * @page: the page to be munlocked