page_counter: track failcnt only for legacy cgroups

Currently page_counter tracks failcnt for counters used by v1 and v2
controllers.  However failcnt is only exported for v1 deployment and thus
there is no need to maintain it in v2.  The oom report does expose failcnt
for memory and swap in v2 but v2 already maintains MEMCG_MAX and
MEMCG_SWAP_MAX event counters which can be used.

Link: https://lkml.kernel.org/r/20250228075808.207484-3-shakeel.butt@linux.dev
Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin (Cruise) <roman.gushchin@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

3 files changed, 27 insertions, 20 deletions

diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c
index bb9578bd99f9..58e895f3899a 100644
--- a/mm/hugetlb_cgroup.c
+++ b/mm/hugetlb_cgroup.c
@@ -101,10 +101,9 @@ static void hugetlb_cgroup_init(struct hugetlb_cgroup *h_cgroup,
 	int idx;
 
 	for (idx = 0; idx < HUGE_MAX_HSTATE; idx++) {
-		struct page_counter *fault_parent = NULL;
-		struct page_counter *rsvd_parent = NULL;
+		struct page_counter *fault, *fault_parent = NULL;
+		struct page_counter *rsvd, *rsvd_parent = NULL;
 		unsigned long limit;
-		int ret;
 
 		if (parent_h_cgroup) {
 			fault_parent = hugetlb_cgroup_counter_from_cgroup(
@@ -112,24 +111,22 @@ static void hugetlb_cgroup_init(struct hugetlb_cgroup *h_cgroup,
 			rsvd_parent = hugetlb_cgroup_counter_from_cgroup_rsvd(
 				parent_h_cgroup, idx);
 		}
-		page_counter_init(hugetlb_cgroup_counter_from_cgroup(h_cgroup,
-								     idx),
-				  fault_parent, false);
-		page_counter_init(
-			hugetlb_cgroup_counter_from_cgroup_rsvd(h_cgroup, idx),
-			rsvd_parent, false);
+		fault = hugetlb_cgroup_counter_from_cgroup(h_cgroup, idx);
+		rsvd = hugetlb_cgroup_counter_from_cgroup_rsvd(h_cgroup, idx);
+
+		page_counter_init(fault, fault_parent, false);
+		page_counter_init(rsvd, rsvd_parent, false);
+
+		if (!cgroup_subsys_on_dfl(hugetlb_cgrp_subsys)) {
+			fault->track_failcnt = true;
+			rsvd->track_failcnt = true;
+		}
 
 		limit = round_down(PAGE_COUNTER_MAX,
 				   pages_per_huge_page(&hstates[idx]));
 
-		ret = page_counter_set_max(
-			hugetlb_cgroup_counter_from_cgroup(h_cgroup, idx),
-			limit);
-		VM_BUG_ON(ret);
-		ret = page_counter_set_max(
-			hugetlb_cgroup_counter_from_cgroup_rsvd(h_cgroup, idx),
-			limit);
-		VM_BUG_ON(ret);
+		VM_BUG_ON(page_counter_set_max(fault, limit));
+		VM_BUG_ON(page_counter_set_max(rsvd, limit));
 	}
 }
 
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9e0e00a2c941..1c496b79de97 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1572,16 +1572,23 @@ void mem_cgroup_print_oom_meminfo(struct mem_cgroup *memcg)
 	/* Use static buffer, for the caller is holding oom_lock. */
 	static char buf[SEQ_BUF_SIZE];
 	struct seq_buf s;
+	unsigned long memory_failcnt;
 
 	lockdep_assert_held(&oom_lock);
 
+	if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
+		memory_failcnt = atomic_long_read(&memcg->memory_events[MEMCG_MAX]);
+	else
+		memory_failcnt = memcg->memory.failcnt;
+
 	pr_info("memory: usage %llukB, limit %llukB, failcnt %lu\n",
 		K((u64)page_counter_read(&memcg->memory)),
-		K((u64)READ_ONCE(memcg->memory.max)), memcg->memory.failcnt);
+		K((u64)READ_ONCE(memcg->memory.max)), memory_failcnt);
 	if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
 		pr_info("swap: usage %llukB, limit %llukB, failcnt %lu\n",
 			K((u64)page_counter_read(&memcg->swap)),
-			K((u64)READ_ONCE(memcg->swap.max)), memcg->swap.failcnt);
+			K((u64)READ_ONCE(memcg->swap.max)),
+			atomic_long_read(&memcg->memory_events[MEMCG_SWAP_MAX]));
 #ifdef CONFIG_MEMCG_V1
 	else {
 		pr_info("memory+swap: usage %llukB, limit %llukB, failcnt %lu\n",
@@ -3631,6 +3638,7 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
 		page_counter_init(&memcg->memory, &parent->memory, memcg_on_dfl);
 		page_counter_init(&memcg->swap, &parent->swap, false);
 #ifdef CONFIG_MEMCG_V1
+		memcg->memory.track_failcnt = !memcg_on_dfl;
 		WRITE_ONCE(memcg->oom_kill_disable, READ_ONCE(parent->oom_kill_disable));
 		page_counter_init(&memcg->kmem, &parent->kmem, false);
 		page_counter_init(&memcg->tcpmem, &parent->tcpmem, false);
diff --git a/mm/page_counter.c b/mm/page_counter.c
index af23f927611b..661e0f2a5127 100644
--- a/mm/page_counter.c
+++ b/mm/page_counter.c
@@ -121,6 +121,7 @@ bool page_counter_try_charge(struct page_counter *counter,
 {
 	struct page_counter *c;
 	bool protection = track_protection(counter);
+	bool track_failcnt = counter->track_failcnt;
 
 	for (c = counter; c; c = c->parent) {
 		long new;
@@ -146,7 +147,8 @@ bool page_counter_try_charge(struct page_counter *counter,
 			 * inaccuracy in the failcnt which is only used
 			 * to report stats.
 			 */
-			data_race(c->failcnt++);
+			if (track_failcnt)
+				data_race(c->failcnt++);
 			*fail = c;
 			goto failed;
 		}