mm/munlock: rmap call mlock_vma_page() munlock_vma_page()

Add vma argument to mlock_vma_page() and munlock_vma_page(), make them
inline functions which check (vma->vm_flags & VM_LOCKED) before calling
mlock_page() and munlock_page() in mm/mlock.c.

Add bool compound to mlock_vma_page() and munlock_vma_page(): this is
because we have understandable difficulty in accounting pte maps of THPs,
and if passed a PageHead page, mlock_page() and munlock_page() cannot
tell whether it's a pmd map to be counted or a pte map to be ignored.

Add vma arg to page_add_file_rmap() and page_remove_rmap(), like the
others, and use that to call mlock_vma_page() at the end of the page
adds, and munlock_vma_page() at the end of page_remove_rmap() (end or
beginning? unimportant, but end was easier for assertions in testing).

No page lock is required (although almost all adds happen to hold it):
delete the "Serialize with page migration" BUG_ON(!PageLocked(page))s.
Certainly page lock did serialize with page migration, but I'm having
difficulty explaining why that was ever important.

Mlock accounting on THPs has been hard to define, differed between anon
and file, involved PageDoubleMap in some places and not others, required
clear_page_mlock() at some points.  Keep it simple now: just count the
pmds and ignore the ptes, there is no reason for ptes to undo pmd mlocks.

page_add_new_anon_rmap() callers unchanged: they have long been calling
lru_cache_add_inactive_or_unevictable(), which does its own VM_LOCKED
handling (it also checks for not VM_SPECIAL: I think that's overcautious,
and inconsistent with other checks, that mmap_region() already prevents
VM_LOCKED on VM_SPECIAL; but haven't quite convinced myself to change it).

Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

1 files changed, 26 insertions, 30 deletions

diff --git a/mm/rmap.c b/mm/rmap.c
index 7ce7f1946cff..6cc8bf129f18 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1181,17 +1181,17 @@ void do_page_add_anon_rmap(struct page *page,
 		__mod_lruvec_page_state(page, NR_ANON_MAPPED, nr);
 	}
 
-	if (unlikely(PageKsm(page))) {
+	if (unlikely(PageKsm(page)))
 		unlock_page_memcg(page);
-		return;
-	}
 
 	/* address might be in next vma when migration races vma_adjust */
-	if (first)
+	else if (first)
 		__page_set_anon_rmap(page, vma, address,
 				flags & RMAP_EXCLUSIVE);
 	else
 		__page_check_anon_rmap(page, vma, address);
+
+	mlock_vma_page(page, vma, compound);
 }
 
 /**
@@ -1232,12 +1232,14 @@ void page_add_new_anon_rmap(struct page *page,
 
 /**
  * page_add_file_rmap - add pte mapping to a file page
- * @page: the page to add the mapping to
- * @compound: charge the page as compound or small page
+ * @page:	the page to add the mapping to
+ * @vma:	the vm area in which the mapping is added
+ * @compound:	charge the page as compound or small page
  *
  * The caller needs to hold the pte lock.
  */
-void page_add_file_rmap(struct page *page, bool compound)
+void page_add_file_rmap(struct page *page,
+	struct vm_area_struct *vma, bool compound)
 {
 	int i, nr = 1;
 
@@ -1260,13 +1262,8 @@ void page_add_file_rmap(struct page *page, bool compound)
 						nr_pages);
 	} else {
 		if (PageTransCompound(page) && page_mapping(page)) {
-			struct page *head = compound_head(page);
-
 			VM_WARN_ON_ONCE(!PageLocked(page));
-
-			SetPageDoubleMap(head);
-			if (PageMlocked(page))
-				clear_page_mlock(head);
+			SetPageDoubleMap(compound_head(page));
 		}
 		if (!atomic_inc_and_test(&page->_mapcount))
 			goto out;
@@ -1274,6 +1271,8 @@ void page_add_file_rmap(struct page *page, bool compound)
 	__mod_lruvec_page_state(page, NR_FILE_MAPPED, nr);
 out:
 	unlock_page_memcg(page);
+
+	mlock_vma_page(page, vma, compound);
 }
 
 static void page_remove_file_rmap(struct page *page, bool compound)
@@ -1368,11 +1367,13 @@ static void page_remove_anon_compound_rmap(struct page *page)
 /**
  * page_remove_rmap - take down pte mapping from a page
  * @page:	page to remove mapping from
+ * @vma:	the vm area from which the mapping is removed
  * @compound:	uncharge the page as compound or small page
  *
  * The caller needs to hold the pte lock.
  */
-void page_remove_rmap(struct page *page, bool compound)
+void page_remove_rmap(struct page *page,
+	struct vm_area_struct *vma, bool compound)
 {
 	lock_page_memcg(page);
 
@@ -1414,6 +1415,8 @@ void page_remove_rmap(struct page *page, bool compound)
 	 */
 out:
 	unlock_page_memcg(page);
+
+	munlock_vma_page(page, vma, compound);
 }
 
 /*
@@ -1469,28 +1472,21 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
 	mmu_notifier_invalidate_range_start(&range);
 
 	while (page_vma_mapped_walk(&pvmw)) {
+		/* Unexpected PMD-mapped THP? */
+		VM_BUG_ON_PAGE(!pvmw.pte, page);
+
 		/*
-		 * If the page is mlock()d, we cannot swap it out.
+		 * If the page is in an mlock()d vma, we must not swap it out.
 		 */
 		if (!(flags & TTU_IGNORE_MLOCK) &&
 		    (vma->vm_flags & VM_LOCKED)) {
-			/*
-			 * PTE-mapped THP are never marked as mlocked: so do
-			 * not set it on a DoubleMap THP, nor on an Anon THP
-			 * (which may still be PTE-mapped after DoubleMap was
-			 * cleared).  But stop unmapping even in those cases.
-			 */
-			if (!PageTransCompound(page) || (PageHead(page) &&
-			     !PageDoubleMap(page) && !PageAnon(page)))
-				mlock_vma_page(page);
+			/* Restore the mlock which got missed */
+			mlock_vma_page(page, vma, false);
 			page_vma_mapped_walk_done(&pvmw);
 			ret = false;
 			break;
 		}
 
-		/* Unexpected PMD-mapped THP? */
-		VM_BUG_ON_PAGE(!pvmw.pte, page);
-
 		subpage = page - page_to_pfn(page) + pte_pfn(*pvmw.pte);
 		address = pvmw.address;
 
@@ -1668,7 +1664,7 @@ discard:
 		 *
 		 * See Documentation/vm/mmu_notifier.rst
 		 */
-		page_remove_rmap(subpage, PageHuge(page));
+		page_remove_rmap(subpage, vma, PageHuge(page));
 		put_page(page);
 	}
 
@@ -1942,7 +1938,7 @@ static bool try_to_migrate_one(struct page *page, struct vm_area_struct *vma,
 		 *
 		 * See Documentation/vm/mmu_notifier.rst
 		 */
-		page_remove_rmap(subpage, PageHuge(page));
+		page_remove_rmap(subpage, vma, PageHuge(page));
 		put_page(page);
 	}
 
@@ -2078,7 +2074,7 @@ static bool page_make_device_exclusive_one(struct page *page,
 		 * There is a reference on the page for the swap entry which has
 		 * been removed, so shouldn't take another.
 		 */
-		page_remove_rmap(subpage, false);
+		page_remove_rmap(subpage, vma, false);
 	}
 
 	mmu_notifier_invalidate_range_end(&range);