Commit 3ac4638a authored by Shakeel Butt's avatar Shakeel Butt Committed by Andrew Morton
Browse files

memcg: make memcg_rstat_updated nmi safe 

Currently kernel maintains memory related stats updates per-cgroup to
optimize stats flushing.  The stats_updates is defined as atomic64_t which
is not nmi-safe on some archs.  Actually we don't really need 64bit atomic
as the max value stats_updates can get should be less than nr_cpus *
MEMCG_CHARGE_BATCH.  A normal atomic_t should suffice.

Also the function cgroup_rstat_updated() is still not nmi-safe but there
is parallel effort to make it nmi-safe, so until then let's ignore it in
the nmi context.

Link: https://lkml.kernel.org/r/20250519063142.111219-6-shakeel.butt@linux.dev


Signed-off-by: default avatarShakeel Butt <shakeel.butt@linux.dev>
Acked-by: default avatarVlastimil 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: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 15ca4fa9

mm/memcontrol.c

+9 −7
Original line number Diff line number Diff line
@@ -531,7 +531,7 @@ struct memcg_vmstats { 
	unsigned long		events_pending[NR_MEMCG_EVENTS];



	/* Stats updates since the last flush */

	atomic64_t		stats_updates;

	atomic_t		stats_updates;

};



/*
@@ -557,7 +557,7 @@ static u64 flush_last_time; 


static bool memcg_vmstats_needs_flush(struct memcg_vmstats *vmstats)

{

	return atomic64_read(&vmstats->stats_updates) >

	return atomic_read(&vmstats->stats_updates) >

		MEMCG_CHARGE_BATCH * num_online_cpus();

}
@@ -571,6 +571,8 @@ static inline void memcg_rstat_updated(struct mem_cgroup *memcg, int val, 
	if (!val)

		return;



	/* TODO: add to cgroup update tree once it is nmi-safe. */

	if (!in_nmi())

		cgroup_rstat_updated(memcg->css.cgroup, cpu);

	statc_pcpu = memcg->vmstats_percpu;

	for (; statc_pcpu; statc_pcpu = statc->parent_pcpu) {
@@ -589,7 +591,7 @@ static inline void memcg_rstat_updated(struct mem_cgroup *memcg, int val, 
			continue;



		stats_updates = this_cpu_xchg(statc_pcpu->stats_updates, 0);

		atomic64_add(stats_updates, &statc->vmstats->stats_updates);

		atomic_add(stats_updates, &statc->vmstats->stats_updates);

	}

}
@@ -597,7 +599,7 @@ static void __mem_cgroup_flush_stats(struct mem_cgroup *memcg, bool force) 
{

	bool needs_flush = memcg_vmstats_needs_flush(memcg->vmstats);



	trace_memcg_flush_stats(memcg, atomic64_read(&memcg->vmstats->stats_updates),

	trace_memcg_flush_stats(memcg, atomic_read(&memcg->vmstats->stats_updates),

		force, needs_flush);



	if (!force && !needs_flush)
@@ -4119,8 +4121,8 @@ static void mem_cgroup_css_rstat_flush(struct cgroup_subsys_state *css, int cpu) 
	}

	WRITE_ONCE(statc->stats_updates, 0);

	/* We are in a per-cpu loop here, only do the atomic write once */

	if (atomic64_read(&memcg->vmstats->stats_updates))

		atomic64_set(&memcg->vmstats->stats_updates, 0);

	if (atomic_read(&memcg->vmstats->stats_updates))

		atomic_set(&memcg->vmstats->stats_updates, 0);

}



static void mem_cgroup_fork(struct task_struct *task)