mm: memcontrol: switch to native NR_ANON_MAPPED counter

Memcg maintains a private MEMCG_RSS counter.  This divergence from the
generic VM accounting means unnecessary code overhead, and creates a
dependency for memcg that page->mapping is set up at the time of charging,
so that page types can be told apart.

Convert the generic accounting sites to mod_lruvec_page_state and friends
to maintain the per-cgroup vmstat counter of NR_ANON_MAPPED.  We use
lock_page_memcg() to stabilize page->mem_cgroup during rmap changes, the
same way we do for NR_FILE_MAPPED.

With the previous patch removing MEMCG_CACHE and the private NR_SHMEM
counter, this patch finally eliminates the need to have page->mapping set
up at charge time.  However, we need to have page->mem_cgroup set up by
the time rmap runs and does the accounting, so switch the commit and the
rmap callbacks around.

v2: fix temporary accounting bug by switching rmap<->commit (Joonsoo)

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Balbir Singh <bsingharora@gmail.com>
Link: http://lkml.kernel.org/r/20200508183105.225460-11-hannes@cmpxchg.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 9 insertions, 18 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ab3497ba0e35..b80125303c02 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -836,13 +836,6 @@ static void mem_cgroup_charge_statistics(struct mem_cgroup *memcg,
 					 struct page *page,
 					 int nr_pages)
 {
-	/*
-	 * Here, RSS means 'mapped anon' and anon's SwapCache. Shmem/tmpfs is
-	 * counted as CACHE even if it's on ANON LRU.
-	 */
-	if (PageAnon(page))
-		__mod_memcg_state(memcg, MEMCG_RSS, nr_pages);
-
 	if (abs(nr_pages) > 1) {
 		VM_BUG_ON_PAGE(!PageTransHuge(page), page);
 		__mod_memcg_state(memcg, MEMCG_RSS_HUGE, nr_pages);
@@ -1384,7 +1377,7 @@ static char *memory_stat_format(struct mem_cgroup *memcg)
 	 */
 
 	seq_buf_printf(&s, "anon %llu\n",
-		       (u64)memcg_page_state(memcg, MEMCG_RSS) *
+		       (u64)memcg_page_state(memcg, NR_ANON_MAPPED) *
 		       PAGE_SIZE);
 	seq_buf_printf(&s, "file %llu\n",
 		       (u64)memcg_page_state(memcg, NR_FILE_PAGES) *
@@ -3353,7 +3346,7 @@ static unsigned long mem_cgroup_usage(struct mem_cgroup *memcg, bool swap)
 
 	if (mem_cgroup_is_root(memcg)) {
 		val = memcg_page_state(memcg, NR_FILE_PAGES) +
-			memcg_page_state(memcg, MEMCG_RSS);
+			memcg_page_state(memcg, NR_ANON_MAPPED);
 		if (swap)
 			val += memcg_page_state(memcg, MEMCG_SWAP);
 	} else {
@@ -3824,7 +3817,7 @@ static int memcg_numa_stat_show(struct seq_file *m, void *v)
 
 static const unsigned int memcg1_stats[] = {
 	NR_FILE_PAGES,
-	MEMCG_RSS,
+	NR_ANON_MAPPED,
 	MEMCG_RSS_HUGE,
 	NR_SHMEM,
 	NR_FILE_MAPPED,
@@ -5455,7 +5448,12 @@ static int mem_cgroup_move_account(struct page *page,
 
 	lock_page_memcg(page);
 
-	if (!PageAnon(page)) {
+	if (PageAnon(page)) {
+		if (page_mapped(page)) {
+			__mod_lruvec_state(from_vec, NR_ANON_MAPPED, -nr_pages);
+			__mod_lruvec_state(to_vec, NR_ANON_MAPPED, nr_pages);
+		}
+	} else {
 		__mod_lruvec_state(from_vec, NR_FILE_PAGES, -nr_pages);
 		__mod_lruvec_state(to_vec, NR_FILE_PAGES, nr_pages);
 
@@ -6589,7 +6587,6 @@ void mem_cgroup_commit_charge(struct page *page, struct mem_cgroup *memcg,
 {
 	unsigned int nr_pages = hpage_nr_pages(page);
 
-	VM_BUG_ON_PAGE(!page->mapping, page);
 	VM_BUG_ON_PAGE(PageLRU(page) && !lrucare, page);
 
 	if (mem_cgroup_disabled())
@@ -6662,8 +6659,6 @@ int mem_cgroup_charge(struct page *page, struct mm_struct *mm, gfp_t gfp_mask,
 	struct mem_cgroup *memcg;
 	int ret;
 
-	VM_BUG_ON_PAGE(!page->mapping, page);
-
 	ret = mem_cgroup_try_charge(page, mm, gfp_mask, &memcg);
 	if (ret)
 		return ret;
@@ -6675,7 +6670,6 @@ struct uncharge_gather {
 	struct mem_cgroup *memcg;
 	unsigned long nr_pages;
 	unsigned long pgpgout;
-	unsigned long nr_anon;
 	unsigned long nr_kmem;
 	unsigned long nr_huge;
 	struct page *dummy_page;
@@ -6700,7 +6694,6 @@ static void uncharge_batch(const struct uncharge_gather *ug)
 	}
 
 	local_irq_save(flags);
-	__mod_memcg_state(ug->memcg, MEMCG_RSS, -ug->nr_anon);
 	__mod_memcg_state(ug->memcg, MEMCG_RSS_HUGE, -ug->nr_huge);
 	__count_memcg_events(ug->memcg, PGPGOUT, ug->pgpgout);
 	__this_cpu_add(ug->memcg->vmstats_percpu->nr_page_events, ug->nr_pages);
@@ -6740,8 +6733,6 @@ static void uncharge_page(struct page *page, struct uncharge_gather *ug)
 	if (!PageKmemcg(page)) {
 		if (PageTransHuge(page))
 			ug->nr_huge += nr_pages;
-		if (PageAnon(page))
-			ug->nr_anon += nr_pages;
 		ug->pgpgout++;
 	} else {
 		ug->nr_kmem += nr_pages;