linux-kernel - [PATCH 3/4] memcg: nmi-safe slab stats updates

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Message-ID: <20250509232859.657525-4-shakeel.butt@linux.dev>
Date: Fri,  9 May 2025 16:28:58 -0700
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...nel.org>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Muchun Song <muchun.song@...ux.dev>,
	Vlastimil Babka <vbabka@...e.cz>,
	Alexei Starovoitov <ast@...nel.org>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	bpf@...r.kernel.org,
	linux-mm@...ck.org,
	cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Meta kernel team <kernel-team@...a.com>
Subject: [PATCH 3/4] memcg: nmi-safe slab stats updates

The objcg based kmem [un]charging can be called in nmi context and it
may need to update NR_SLAB_[UN]RECLAIMABLE_B stats. So, let's correctly
handle the updates of these stats in the nmi context.

Signed-off-by: Shakeel Butt <shakeel.butt@...ux.dev>
---
 mm/memcontrol.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e91e4368650f..bba549c1f18c 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2591,8 +2591,18 @@ static inline void __mod_objcg_mlstate(struct obj_cgroup *objcg,
 
 	rcu_read_lock();
 	memcg = obj_cgroup_memcg(objcg);
-	lruvec = mem_cgroup_lruvec(memcg, pgdat);
-	__mod_memcg_lruvec_state(lruvec, idx, nr);
+	if (likely(!in_nmi())) {
+		lruvec = mem_cgroup_lruvec(memcg, pgdat);
+		__mod_memcg_lruvec_state(lruvec, idx, nr);
+	} else {
+		struct mem_cgroup_per_node *pn = memcg->nodeinfo[pgdat->node_id];
+
+		/* TODO: add to cgroup update tree once it is nmi-safe. */
+		if (idx == NR_SLAB_RECLAIMABLE_B)
+			atomic64_add(nr, &pn->slab_reclaimable);
+		else
+			atomic64_add(nr, &pn->slab_unreclaimable);
+	}
 	rcu_read_unlock();
 }
 
-- 
2.47.1