memcg: nmi safe memcg stats for specific archs

There are archs which have NMI but does not support this_cpu_* ops safely
in the nmi context but they support safe atomic ops in nmi context.  For
such archs, let's add infra to use atomic ops for the memcg stats which
can be updated in nmi.

At the moment, the memcg stats which get updated in the objcg charging
path are MEMCG_KMEM, NR_SLAB_RECLAIMABLE_B & NR_SLAB_UNRECLAIMABLE_B.
Rather than adding support for all memcg stats to be nmi safe, let's just
add infra to make these three stats nmi safe which this patch is doing.

Link: https://lkml.kernel.org/r/20250519063142.111219-3-shakeel.butt@linux.dev
Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index f7848f73f41c0c7a3d05ab0fa7058e541db72e8f..87b6688f124a7d78135d1d9dd4c641d825446ac6 100644 (file)
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -113,6 +113,12 @@ struct mem_cgroup_per_node {
        CACHELINE_PADDING(_pad2_);
        unsigned long           lru_zone_size[MAX_NR_ZONES][NR_LRU_LISTS];
        struct mem_cgroup_reclaim_iter  iter;
+
+#ifdef CONFIG_MEMCG_NMI_SAFETY_REQUIRES_ATOMIC
+       /* slab stats for nmi context */
+       atomic_t                slab_reclaimable;
+       atomic_t                slab_unreclaimable;
+#endif
 };
 
 struct mem_cgroup_threshold {
@@ -236,6 +242,10 @@ struct mem_cgroup {
        atomic_long_t           memory_events[MEMCG_NR_MEMORY_EVENTS];
        atomic_long_t           memory_events_local[MEMCG_NR_MEMORY_EVENTS];
 
+#ifdef CONFIG_MEMCG_NMI_SAFETY_REQUIRES_ATOMIC
+       /* MEMCG_KMEM for nmi context */
+       atomic_t                kmem_stat;
+#endif
        /*
         * Hint of reclaim pressure for socket memroy management. Note
         * that this indicator should NOT be used in legacy cgroup mode

diff --git a/init/Kconfig b/init/Kconfig
index a2aa49cfb8bd85f990d1a947f5718c52b167c428..e9f47baa34e0ad6d66d418af63ab9d325add582b 100644 (file)
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1013,6 +1013,13 @@ config MEMCG_NMI_UNSAFE
        depends on !ARCH_HAS_NMI_SAFE_THIS_CPU_OPS && !ARCH_HAVE_NMI_SAFE_CMPXCHG
        default y
 
+config MEMCG_NMI_SAFETY_REQUIRES_ATOMIC
+       bool
+       depends on MEMCG
+       depends on HAVE_NMI
+       depends on !ARCH_HAS_NMI_SAFE_THIS_CPU_OPS && ARCH_HAVE_NMI_SAFE_CMPXCHG
+       default y
+
 config MEMCG_V1
        bool "Legacy cgroup v1 memory controller"
        depends on MEMCG

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 2532cc2316ee39e201d6e3439ab131bb98567729..e8e8becbe92653d8509946ee1d866a756875f46f 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3966,6 +3966,53 @@ static void mem_cgroup_stat_aggregate(struct aggregate_control *ac)
        }
 }
 
+#ifdef CONFIG_MEMCG_NMI_SAFETY_REQUIRES_ATOMIC
+static void flush_nmi_stats(struct mem_cgroup *memcg, struct mem_cgroup *parent,
+                           int cpu)
+{
+       int nid;
+
+       if (atomic_read(&memcg->kmem_stat)) {
+               int kmem = atomic_xchg(&memcg->kmem_stat, 0);
+               int index = memcg_stats_index(MEMCG_KMEM);
+
+               memcg->vmstats->state[index] += kmem;
+               if (parent)
+                       parent->vmstats->state_pending[index] += kmem;
+       }
+
+       for_each_node_state(nid, N_MEMORY) {
+               struct mem_cgroup_per_node *pn = memcg->nodeinfo[nid];
+               struct lruvec_stats *lstats = pn->lruvec_stats;
+               struct lruvec_stats *plstats = NULL;
+
+               if (parent)
+                       plstats = parent->nodeinfo[nid]->lruvec_stats;
+
+               if (atomic_read(&pn->slab_reclaimable)) {
+                       int slab = atomic_xchg(&pn->slab_reclaimable, 0);
+                       int index = memcg_stats_index(NR_SLAB_RECLAIMABLE_B);
+
+                       lstats->state[index] += slab;
+                       if (plstats)
+                               plstats->state_pending[index] += slab;
+               }
+               if (atomic_read(&pn->slab_unreclaimable)) {
+                       int slab = atomic_xchg(&pn->slab_unreclaimable, 0);
+                       int index = memcg_stats_index(NR_SLAB_UNRECLAIMABLE_B);
+
+                       lstats->state[index] += slab;
+                       if (plstats)
+                               plstats->state_pending[index] += slab;
+               }
+       }
+}
+#else
+static void flush_nmi_stats(struct mem_cgroup *memcg, struct mem_cgroup *parent,
+                           int cpu)
+{}
+#endif
+
 static void mem_cgroup_css_rstat_flush(struct cgroup_subsys_state *css, int cpu)
 {
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);
@@ -3974,6 +4021,8 @@ static void mem_cgroup_css_rstat_flush(struct cgroup_subsys_state *css, int cpu)
        struct aggregate_control ac;
        int nid;
 
+       flush_nmi_stats(memcg, parent, cpu);
+
        statc = per_cpu_ptr(memcg->vmstats_percpu, cpu);
 
        ac = (struct aggregate_control) {