Re: [PATCH bpf-next v5 06/34] bpf: prepare for memcg-based memory accounting for bpf maps

[Song Liu <songliubraving@xxxxxx>]

> On Nov 12, 2020, at 2:15 PM, Roman Gushchin <guro@xxxxxx> wrote:

[...]

> 
> +#ifdef CONFIG_MEMCG_KMEM
> +static __always_inline int __bpf_map_update_elem(struct bpf_map *map, void *key,
> +						 void *value, u64 flags)
> +{
> +	struct mem_cgroup *old_memcg;
> +	bool in_interrupt;
> +	int ret;
> +
> +	/*
> +	 * If update from an interrupt context results in a memory allocation,
> +	 * the memory cgroup to charge can't be determined from the context
> +	 * of the current task. Instead, we charge the memory cgroup, which
> +	 * contained a process created the map.
> +	 */
> +	in_interrupt = in_interrupt();
> +	if (in_interrupt)
> +		old_memcg = set_active_memcg(map->memcg);

set_active_memcg() checks in_interrupt() again. Maybe we can introduce another
helper to avoid checking it twice? Something like

static inline struct mem_cgroup *
set_active_memcg_int(struct mem_cgroup *memcg)
{
        struct mem_cgroup *old;

        old = this_cpu_read(int_active_memcg);
        this_cpu_write(int_active_memcg, memcg);
        return old;
}

Thanks,
Song

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