mm: rmap: remove lock_page_memcg()

The previous patch made sure charge moving only touches pages for which
page_mapped() is stable.  lock_page_memcg() is no longer needed.

Link: https://lkml.kernel.org/r/20221206171340.139790-3-hannes@cmpxchg.orgSigned-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Hugh Dickins <hughd@google.com>
Acked-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/rmap.c

@@ -1222,9 +1222,6 @@ void page_add_anon_rmap(struct page *page,
 	bool compound = flags & RMAP_COMPOUND;
 	bool first = true;
 
-	if (unlikely(PageKsm(page)))
-		lock_page_memcg(page);
-
 	/* Is page being mapped by PTE? Is this its first map to be added? */
 	if (likely(!compound)) {
 		first = atomic_inc_and_test(&page->_mapcount);
@@ -1262,15 +1259,14 @@ void page_add_anon_rmap(struct page *page,
 	if (nr)
 		__mod_lruvec_page_state(page, NR_ANON_MAPPED, nr);
 
-	if (unlikely(PageKsm(page)))
-		unlock_page_memcg(page);
-
+	if (likely(!PageKsm(page))) {
 		/* address might be in next vma when migration races vma_adjust */
-	else if (first)
+		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);
 }
@@ -1329,7 +1325,6 @@ void page_add_file_rmap(struct page *page,
 	bool first;
 
 	VM_BUG_ON_PAGE(compound && !PageTransHuge(page), page);
-	lock_page_memcg(page);
 
 	/* Is page being mapped by PTE? Is this its first map to be added? */
 	if (likely(!compound)) {
@@ -1365,7 +1360,6 @@ void page_add_file_rmap(struct page *page,
 			NR_SHMEM_PMDMAPPED : NR_FILE_PMDMAPPED, nr_pmdmapped);
 	if (nr)
 		__mod_lruvec_page_state(page, NR_FILE_MAPPED, nr);
-	unlock_page_memcg(page);
 
 	mlock_vma_page(page, vma, compound);
 }
@@ -1394,8 +1388,6 @@ void page_remove_rmap(struct page *page,
 		return;
 	}
 
-	lock_page_memcg(page);
-
 	/* Is page being unmapped by PTE? Is this its last map to be removed? */
 	if (likely(!compound)) {
 		last = atomic_add_negative(-1, &page->_mapcount);
@@ -1451,8 +1443,6 @@ void page_remove_rmap(struct page *page,
 	 * and remember that it's only reliable while mapped.
 	 */
 
-	unlock_page_memcg(page);
-
 	munlock_vma_page(page, vma, compound);
 }