mm: rmap: split out page_remove_file_rmap()

page_remove_rmap() has too many branches on PageAnon() and is hard to
follow.  Move the file part into a separate function.
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Cc: Vladimir Davydov <vdavydov@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/rmap.c

@@ -1054,6 +1054,36 @@ void page_add_file_rmap(struct page *page)
 	mem_cgroup_end_page_stat(memcg, locked, flags);
 }
 
+static void page_remove_file_rmap(struct page *page)
+{
+	struct mem_cgroup *memcg;
+	unsigned long flags;
+	bool locked;
+
+	memcg = mem_cgroup_begin_page_stat(page, &locked, &flags);
+
+	/* page still mapped by someone else? */
+	if (!atomic_add_negative(-1, &page->_mapcount))
+		goto out;
+
+	/* Hugepages are not counted in NR_FILE_MAPPED for now. */
+	if (unlikely(PageHuge(page)))
+		goto out;
+
+	/*
+	 * We use the irq-unsafe __{inc|mod}_zone_page_stat because
+	 * these counters are not modified in interrupt context, and
+	 * pte lock(a spinlock) is held, which implies preemption disabled.
+	 */
+	__dec_zone_page_state(page, NR_FILE_MAPPED);
+	mem_cgroup_dec_page_stat(memcg, MEM_CGROUP_STAT_FILE_MAPPED);
+
+	if (unlikely(PageMlocked(page)))
+		clear_page_mlock(page);
+out:
+	mem_cgroup_end_page_stat(memcg, locked, flags);
+}
+
 /**
  * page_remove_rmap - take down pte mapping from a page
  * @page: page to remove mapping from
@@ -1062,46 +1092,33 @@ void page_add_file_rmap(struct page *page)
  */
 void page_remove_rmap(struct page *page)
 {
-	struct mem_cgroup *uninitialized_var(memcg);
-	bool anon = PageAnon(page);
-	unsigned long flags;
-	bool locked;
-
-	/*
-	 * The anon case has no mem_cgroup page_stat to update; but may
-	 * uncharge_page() below, where the lock ordering can deadlock if
-	 * we hold the lock against page_stat move: so avoid it on anon.
-	 */
-	if (!anon)
-		memcg = mem_cgroup_begin_page_stat(page, &locked, &flags);
+	if (!PageAnon(page)) {
+		page_remove_file_rmap(page);
+		return;
+	}
 
 	/* page still mapped by someone else? */
 	if (!atomic_add_negative(-1, &page->_mapcount))
-		goto out;
+		return;
+
+	/* Hugepages are not counted in NR_ANON_PAGES for now. */
+	if (unlikely(PageHuge(page)))
+		return;
 
 	/*
-	 * Hugepages are not counted in NR_ANON_PAGES nor NR_FILE_MAPPED
-	 * and not charged by memcg for now.
-	 *
 	 * We use the irq-unsafe __{inc|mod}_zone_page_stat because
 	 * these counters are not modified in interrupt context, and
-	 * these counters are not modified in interrupt context, and
 	 * pte lock(a spinlock) is held, which implies preemption disabled.
 	 */
-	if (unlikely(PageHuge(page)))
-		goto out;
-	if (anon) {
 	if (PageTransHuge(page))
-			__dec_zone_page_state(page,
-					      NR_ANON_TRANSPARENT_HUGEPAGES);
+		__dec_zone_page_state(page, NR_ANON_TRANSPARENT_HUGEPAGES);
+
 	__mod_zone_page_state(page_zone(page), NR_ANON_PAGES,
 			      -hpage_nr_pages(page));
-	} else {
-		__dec_zone_page_state(page, NR_FILE_MAPPED);
-		mem_cgroup_dec_page_stat(memcg, MEM_CGROUP_STAT_FILE_MAPPED);
-	}
+
 	if (unlikely(PageMlocked(page)))
 		clear_page_mlock(page);
+
 	/*
 	 * It would be tidy to reset the PageAnon mapping here,
 	 * but that might overwrite a racing page_add_anon_rmap
@@ -1111,9 +1128,6 @@ void page_remove_rmap(struct page *page)
 	 * Leaving it set also helps swapoff to reinstate ptes
 	 * faster for those pages still in swapcache.
 	 */
-out:
-	if (!anon)
-		mem_cgroup_end_page_stat(memcg, locked, flags);
 }
 
 /*