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

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Message-ID: <3645417A-F356-4422-B336-874DFEB74014@fb.com>
Date:   Fri, 13 Nov 2020 17:46:49 +0000
From:   Song Liu <songliubraving@...com>
To:     Roman Gushchin <guro@...com>
CC:     bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        "Daniel Borkmann" <daniel@...earbox.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH bpf-next v5 06/34] bpf: prepare for memcg-based memory
 accounting for bpf maps



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

[...]