diff --git a/include/linux/mm.h b/include/linux/mm.h
index 70f59de..67e0fab 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -410,6 +410,19 @@
 
 extern void kvfree(const void *addr);
 
+static inline atomic_t *compound_mapcount_ptr(struct page *page)
+{
+	return &page[1].compound_mapcount;
+}
+
+static inline int compound_mapcount(struct page *page)
+{
+	if (!PageCompound(page))
+		return 0;
+	page = compound_head(page);
+	return atomic_read(compound_mapcount_ptr(page)) + 1;
+}
+
 /*
  * The atomic page->_mapcount, starts from -1: so that transitions
  * both from it and to it can be tracked, using atomic_inc_and_test
@@ -422,8 +435,17 @@
 
 static inline int page_mapcount(struct page *page)
 {
+	int ret;
 	VM_BUG_ON_PAGE(PageSlab(page), page);
-	return atomic_read(&page->_mapcount) + 1;
+
+	ret = atomic_read(&page->_mapcount) + 1;
+	if (PageCompound(page)) {
+		page = compound_head(page);
+		ret += atomic_read(compound_mapcount_ptr(page)) + 1;
+		if (PageDoubleMap(page))
+			ret--;
+	}
+	return ret;
 }
 
 static inline int page_count(struct page *page)
@@ -934,7 +956,7 @@
  */
 static inline int page_mapped(struct page *page)
 {
-	return atomic_read(&(page)->_mapcount) >= 0;
+	return atomic_read(&(page)->_mapcount) + compound_mapcount(page) >= 0;
 }
 
 /*
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index faf6fe8..809defe 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -54,6 +54,7 @@
 						 * see PAGE_MAPPING_ANON below.
 						 */
 		void *s_mem;			/* slab first object */
+		atomic_t compound_mapcount;	/* first tail page */
 	};
 
 	/* Second double word */
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 0c42acc..19724e6 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -126,6 +126,9 @@
 
 	/* SLOB */
 	PG_slob_free = PG_private,
+
+	/* Compound pages. Stored in first tail page's flags */
+	PG_double_map = PG_private_2,
 };
 
 #ifndef __GENERATING_BOUNDS_H
@@ -523,10 +526,43 @@
 	return PageTail(page);
 }
 
+/*
+ * PageDoubleMap indicates that the compound page is mapped with PTEs as well
+ * as PMDs.
+ *
+ * This is required for optimization of rmap operations for THP: we can postpone
+ * per small page mapcount accounting (and its overhead from atomic operations)
+ * until the first PMD split.
+ *
+ * For the page PageDoubleMap means ->_mapcount in all sub-pages is offset up
+ * by one. This reference will go away with last compound_mapcount.
+ *
+ * See also __split_huge_pmd_locked() and page_remove_anon_compound_rmap().
+ */
+static inline int PageDoubleMap(struct page *page)
+{
+	return PageHead(page) && test_bit(PG_double_map, &page[1].flags);
+}
+
+static inline int TestSetPageDoubleMap(struct page *page)
+{
+	VM_BUG_ON_PAGE(!PageHead(page), page);
+	return test_and_set_bit(PG_double_map, &page[1].flags);
+}
+
+static inline int TestClearPageDoubleMap(struct page *page)
+{
+	VM_BUG_ON_PAGE(!PageHead(page), page);
+	return test_and_clear_bit(PG_double_map, &page[1].flags);
+}
+
 #else
 TESTPAGEFLAG_FALSE(TransHuge)
 TESTPAGEFLAG_FALSE(TransCompound)
 TESTPAGEFLAG_FALSE(TransTail)
+TESTPAGEFLAG_FALSE(DoubleMap)
+	TESTSETFLAG_FALSE(DoubleMap)
+	TESTCLEARFLAG_FALSE(DoubleMap)
 #endif
 
 /*
diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 038b6e7..ebf3750 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -183,9 +183,9 @@
 void hugepage_add_new_anon_rmap(struct page *, struct vm_area_struct *,
 				unsigned long);
 
-static inline void page_dup_rmap(struct page *page)
+static inline void page_dup_rmap(struct page *page, bool compound)
 {
-	atomic_inc(&page->_mapcount);
+	atomic_inc(compound ? compound_mapcount_ptr(page) : &page->_mapcount);
 }
 
 /*
diff --git a/mm/debug.c b/mm/debug.c
index 03c9a13..f05b2d5 100644
--- a/mm/debug.c
+++ b/mm/debug.c
@@ -79,9 +79,12 @@
 void dump_page_badflags(struct page *page, const char *reason,
 		unsigned long badflags)
 {
-	pr_emerg("page:%p count:%d mapcount:%d mapping:%p index:%#lx\n",
+	pr_emerg("page:%p count:%d mapcount:%d mapping:%p index:%#lx",
 		  page, atomic_read(&page->_count), page_mapcount(page),
 		  page->mapping, page->index);
+	if (PageCompound(page))
+		pr_cont(" compound_mapcount: %d", compound_mapcount(page));
+	pr_cont("\n");
 	BUILD_BUG_ON(ARRAY_SIZE(pageflag_names) != __NR_PAGEFLAGS);
 	dump_flags(page->flags, pageflag_names, ARRAY_SIZE(pageflag_names));
 	if (reason)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 1de7ab5..1588f68 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -989,7 +989,7 @@
 	src_page = pmd_page(pmd);
 	VM_BUG_ON_PAGE(!PageHead(src_page), src_page);
 	get_page(src_page);
-	page_dup_rmap(src_page);
+	page_dup_rmap(src_page, true);
 	add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR);
 
 	pmdp_set_wrprotect(src_mm, addr, src_pmd);
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 84af842..12908dc 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3102,7 +3102,7 @@
 			entry = huge_ptep_get(src_pte);
 			ptepage = pte_page(entry);
 			get_page(ptepage);
-			page_dup_rmap(ptepage);
+			page_dup_rmap(ptepage, true);
 			set_huge_pte_at(dst, addr, dst_pte, entry);
 			hugetlb_count_add(pages_per_huge_page(h), dst);
 		}
@@ -3585,7 +3585,7 @@
 		ClearPagePrivate(page);
 		hugepage_add_new_anon_rmap(page, vma, address);
 	} else
-		page_dup_rmap(page);
+		page_dup_rmap(page, true);
 	new_pte = make_huge_pte(vma, page, ((vma->vm_flags & VM_WRITE)
 				&& (vma->vm_flags & VM_SHARED)));
 	set_huge_pte_at(mm, address, ptep, new_pte);
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 3b8c845..bee6b1c 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4899,6 +4899,14 @@
 		switch (get_mctgt_type(vma, addr, ptent, &target)) {
 		case MC_TARGET_PAGE:
 			page = target.page;
+			/*
+			 * We can have a part of the split pmd here. Moving it
+			 * can be done but it would be too convoluted so simply
+			 * ignore such a partial THP and keep it in original
+			 * memcg. There should be somebody mapping the head.
+			 */
+			if (PageTransCompound(page))
+				goto put;
 			if (isolate_lru_page(page))
 				goto put;
 			if (!mem_cgroup_move_account(page, false,
diff --git a/mm/memory.c b/mm/memory.c
index 3b656d1..9b0dbc2 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -864,7 +864,7 @@
 	page = vm_normal_page(vma, addr, pte);
 	if (page) {
 		get_page(page);
-		page_dup_rmap(page);
+		page_dup_rmap(page, false);
 		rss[mm_counter(page)]++;
 	}
 
diff --git a/mm/migrate.c b/mm/migrate.c
index 3921f20..91545da 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -165,7 +165,7 @@
 		if (PageAnon(new))
 			hugepage_add_anon_rmap(new, vma, addr);
 		else
-			page_dup_rmap(new);
+			page_dup_rmap(new, true);
 	} else if (PageAnon(new))
 		page_add_anon_rmap(new, vma, addr, false);
 	else
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d02d643..3221091 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -469,6 +469,7 @@
 		p->mapping = TAIL_MAPPING;
 		set_compound_head(p, page);
 	}
+	atomic_set(compound_mapcount_ptr(page), -1);
 }
 
 #ifdef CONFIG_DEBUG_PAGEALLOC
@@ -733,7 +734,7 @@
 	const char *bad_reason = NULL;
 	unsigned long bad_flags = 0;
 
-	if (unlikely(page_mapcount(page)))
+	if (unlikely(atomic_read(&page->_mapcount) != -1))
 		bad_reason = "nonzero mapcount";
 	if (unlikely(page->mapping != NULL))
 		bad_reason = "non-NULL mapping";
@@ -857,7 +858,13 @@
 		ret = 0;
 		goto out;
 	}
-	if (page->mapping != TAIL_MAPPING) {
+	/* mapping in first tail page is used for compound_mapcount() */
+	if (page - head_page == 1) {
+		if (unlikely(compound_mapcount(page))) {
+			bad_page(page, "nonzero compound_mapcount", 0);
+			goto out;
+		}
+	} else if (page->mapping != TAIL_MAPPING) {
 		bad_page(page, "corrupted mapping in tail page", 0);
 		goto out;
 	}
@@ -1335,7 +1342,7 @@
 	const char *bad_reason = NULL;
 	unsigned long bad_flags = 0;
 
-	if (unlikely(page_mapcount(page)))
+	if (unlikely(atomic_read(&page->_mapcount) != -1))
 		bad_reason = "nonzero mapcount";
 	if (unlikely(page->mapping != NULL))
 		bad_reason = "non-NULL mapping";
diff --git a/mm/rmap.c b/mm/rmap.c
index aa68a40..2e62571 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1122,7 +1122,7 @@
 	 * over the call to page_add_new_anon_rmap.
 	 */
 	BUG_ON(page_anon_vma(page)->root != vma->anon_vma->root);
-	BUG_ON(page->index != linear_page_index(vma, address));
+	BUG_ON(page_to_pgoff(page) != linear_page_index(vma, address));
 #endif
 }
 
@@ -1152,9 +1152,28 @@
 void do_page_add_anon_rmap(struct page *page,
 	struct vm_area_struct *vma, unsigned long address, int flags)
 {
-	int first = atomic_inc_and_test(&page->_mapcount);
+	bool compound = flags & RMAP_COMPOUND;
+	bool first;
+
+	if (PageTransCompound(page)) {
+		VM_BUG_ON_PAGE(!PageLocked(page), page);
+		if (compound) {
+			atomic_t *mapcount;
+
+			VM_BUG_ON_PAGE(!PageTransHuge(page), page);
+			mapcount = compound_mapcount_ptr(page);
+			first = atomic_inc_and_test(mapcount);
+		} else {
+			/* Anon THP always mapped first with PMD */
+			first = 0;
+			VM_BUG_ON_PAGE(!page_mapcount(page), page);
+			atomic_inc(&page->_mapcount);
+		}
+	} else {
+		first = atomic_inc_and_test(&page->_mapcount);
+	}
+
 	if (first) {
-		bool compound = flags & RMAP_COMPOUND;
 		int nr = compound ? hpage_nr_pages(page) : 1;
 		/*
 		 * We use the irq-unsafe __{inc|mod}_zone_page_stat because
@@ -1173,6 +1192,7 @@
 		return;
 
 	VM_BUG_ON_PAGE(!PageLocked(page), page);
+
 	/* address might be in next vma when migration races vma_adjust */
 	if (first)
 		__page_set_anon_rmap(page, vma, address,
@@ -1199,10 +1219,16 @@
 
 	VM_BUG_ON_VMA(address < vma->vm_start || address >= vma->vm_end, vma);
 	SetPageSwapBacked(page);
-	atomic_set(&page->_mapcount, 0); /* increment count (starts at -1) */
 	if (compound) {
 		VM_BUG_ON_PAGE(!PageTransHuge(page), page);
+		/* increment count (starts at -1) */
+		atomic_set(compound_mapcount_ptr(page), 0);
 		__inc_zone_page_state(page, NR_ANON_TRANSPARENT_HUGEPAGES);
+	} else {
+		/* Anon THP always mapped first with PMD */
+		VM_BUG_ON_PAGE(PageTransCompound(page), page);
+		/* increment count (starts at -1) */
+		atomic_set(&page->_mapcount, 0);
 	}
 	__mod_zone_page_state(page_zone(page), NR_ANON_PAGES, nr);
 	__page_set_anon_rmap(page, vma, address, 1);
@@ -1232,14 +1258,17 @@
 
 	memcg = mem_cgroup_begin_page_stat(page);
 
+	/* Hugepages are not counted in NR_FILE_MAPPED for now. */
+	if (unlikely(PageHuge(page))) {
+		/* hugetlb pages are always mapped with pmds */
+		atomic_dec(compound_mapcount_ptr(page));
+		goto out;
+	}
+
 	/* 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
@@ -1254,6 +1283,39 @@
 	mem_cgroup_end_page_stat(memcg);
 }
 
+static void page_remove_anon_compound_rmap(struct page *page)
+{
+	int i, nr;
+
+	if (!atomic_add_negative(-1, compound_mapcount_ptr(page)))
+		return;
+
+	/* Hugepages are not counted in NR_ANON_PAGES for now. */
+	if (unlikely(PageHuge(page)))
+		return;
+
+	if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
+		return;
+
+	__dec_zone_page_state(page, NR_ANON_TRANSPARENT_HUGEPAGES);
+
+	if (TestClearPageDoubleMap(page)) {
+		/*
+		 * Subpages can be mapped with PTEs too. Check how many of
+		 * themi are still mapped.
+		 */
+		for (i = 0, nr = 0; i < HPAGE_PMD_NR; i++) {
+			if (atomic_add_negative(-1, &page[i]._mapcount))
+				nr++;
+		}
+	} else {
+		nr = HPAGE_PMD_NR;
+	}
+
+	if (nr)
+		__mod_zone_page_state(page_zone(page), NR_ANON_PAGES, -nr);
+}
+
 /**
  * page_remove_rmap - take down pte mapping from a page
  * @page:	page to remove mapping from
@@ -1263,33 +1325,25 @@
  */
 void page_remove_rmap(struct page *page, bool compound)
 {
-	int nr = compound ? hpage_nr_pages(page) : 1;
-
 	if (!PageAnon(page)) {
 		VM_BUG_ON_PAGE(compound && !PageHuge(page), page);
 		page_remove_file_rmap(page);
 		return;
 	}
 
+	if (compound)
+		return page_remove_anon_compound_rmap(page);
+
 	/* page still mapped by someone else? */
 	if (!atomic_add_negative(-1, &page->_mapcount))
 		return;
 
-	/* Hugepages are not counted in NR_ANON_PAGES for now. */
-	if (unlikely(PageHuge(page)))
-		return;
-
 	/*
 	 * 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.
 	 */
-	if (compound) {
-		VM_BUG_ON_PAGE(!PageTransHuge(page), page);
-		__dec_zone_page_state(page, NR_ANON_TRANSPARENT_HUGEPAGES);
-	}
-
-	__mod_zone_page_state(page_zone(page), NR_ANON_PAGES, -nr);
+	__dec_zone_page_state(page, NR_ANON_PAGES);
 
 	if (unlikely(PageMlocked(page)))
 		clear_page_mlock(page);
@@ -1710,7 +1764,7 @@
 	BUG_ON(!PageLocked(page));
 	BUG_ON(!anon_vma);
 	/* address might be in next vma when migration races vma_adjust */
-	first = atomic_inc_and_test(&page->_mapcount);
+	first = atomic_inc_and_test(compound_mapcount_ptr(page));
 	if (first)
 		__hugepage_set_anon_rmap(page, vma, address, 0);
 }
@@ -1719,7 +1773,7 @@
 			struct vm_area_struct *vma, unsigned long address)
 {
 	BUG_ON(address < vma->vm_start || address >= vma->vm_end);
-	atomic_set(&page->_mapcount, 0);
+	atomic_set(compound_mapcount_ptr(page), 0);
 	__hugepage_set_anon_rmap(page, vma, address, 1);
 }
 #endif /* CONFIG_HUGETLB_PAGE */