mm: memcontrol: convert NR_SHMEM_PMDMAPPED account to pages

Currently we use struct per_cpu_nodestat to cache the vmstat counters,
which leads to inaccurate statistics especially THP vmstat counters.  In
the systems with hundreds of processors it can be GBs of memory.  For
example, for a 96 CPUs system, the threshold is the maximum number of 125.
And the per cpu counters can cache 23.4375 GB in total.

The THP page is already a form of batched addition (it will add 512 worth
of memory in one go) so skipping the batching seems like sensible.
Although every THP stats update overflows the per-cpu counter, resorting
to atomic global updates.  But it can make the statistics more accuracy
for the THP vmstat counters.

So we convert the NR_SHMEM_PMDMAPPED account to pages.  This patch is
consistent with 8f182270dfec ("mm/swap.c: flush lru pvecs on compound page
arrival").  Doing this also can make the unit of vmstat counters more
unified.  Finally, the unit of the vmstat counters are pages, kB and
bytes.  The B/KB suffix can tell us that the unit is bytes or kB.  The
rest which is without suffix are pages.

Link: https://lkml.kernel.org/r/20201228164110.2838-6-songmuchun@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Feng Tang <feng.tang@intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: NeilBrown <neilb@suse.de>
Cc: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>
Cc: Rafael. J. Wysocki <rafael@kernel.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Roman Gushchin <guro@fb.com>
Cc: Sami Tolvanen <samitolvanen@google.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 11 insertions, 6 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index df292d8e659b..069561aadc7b 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5585,8 +5585,7 @@ void show_free_areas(unsigned int filter, nodemask_t *nodemask)
 			K(node_page_state(pgdat, NR_SHMEM)),
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 			K(node_page_state(pgdat, NR_SHMEM_THPS)),
-			K(node_page_state(pgdat, NR_SHMEM_PMDMAPPED)
-					* HPAGE_PMD_NR),
+			K(node_page_state(pgdat, NR_SHMEM_PMDMAPPED)),
 			K(node_page_state(pgdat, NR_ANON_THPS)),
 #endif
 			K(node_page_state(pgdat, NR_WRITEBACK_TEMP)),
diff --git a/mm/rmap.c b/mm/rmap.c
index c4d5c63cfd29..1c1b576c0627 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1211,14 +1211,17 @@ void page_add_file_rmap(struct page *page, bool compound)
 	VM_BUG_ON_PAGE(compound && !PageTransHuge(page), page);
 	lock_page_memcg(page);
 	if (compound && PageTransHuge(page)) {
-		for (i = 0, nr = 0; i < thp_nr_pages(page); i++) {
+		int nr_pages = thp_nr_pages(page);
+
+		for (i = 0, nr = 0; i < nr_pages; i++) {
 			if (atomic_inc_and_test(&page[i]._mapcount))
 				nr++;
 		}
 		if (!atomic_inc_and_test(compound_mapcount_ptr(page)))
 			goto out;
 		if (PageSwapBacked(page))
-			__inc_node_page_state(page, NR_SHMEM_PMDMAPPED);
+			__mod_lruvec_page_state(page, NR_SHMEM_PMDMAPPED,
+						nr_pages);
 		else
 			__inc_node_page_state(page, NR_FILE_PMDMAPPED);
 	} else {
@@ -1252,14 +1255,17 @@ static void page_remove_file_rmap(struct page *page, bool compound)
 
 	/* page still mapped by someone else? */
 	if (compound && PageTransHuge(page)) {
-		for (i = 0, nr = 0; i < thp_nr_pages(page); i++) {
+		int nr_pages = thp_nr_pages(page);
+
+		for (i = 0, nr = 0; i < nr_pages; i++) {
 			if (atomic_add_negative(-1, &page[i]._mapcount))
 				nr++;
 		}
 		if (!atomic_add_negative(-1, compound_mapcount_ptr(page)))
 			return;
 		if (PageSwapBacked(page))
-			__dec_node_page_state(page, NR_SHMEM_PMDMAPPED);
+			__mod_lruvec_page_state(page, NR_SHMEM_PMDMAPPED,
+						-nr_pages);
 		else
 			__dec_node_page_state(page, NR_FILE_PMDMAPPED);
 	} else {