Re: [PATCH v2 6/6] zswap: memcg accounting

From: Shakeel Butt <shakeelb@google.com>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Michal Hocko <mhocko@suse.com>, Roman Gushchin <guro@fb.com>,
	Seth Jennings <sjenning@redhat.com>,
	Dan Streetman <ddstreet@ieee.org>,
	Minchan Kim <minchan@kernel.org>, Linux MM <linux-mm@kvack.org>,
	Cgroups <cgroups@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Kernel Team <kernel-team@fb.com>
Subject: Re: [PATCH v2 6/6] zswap: memcg accounting
Date: Fri, 13 May 2022 10:23:36 -0700	[thread overview]
Message-ID: <CALvZod6kBZZFfD6Y5p_=9TMJr8P-vU_77NTq048wGUDr0wTv0Q@mail.gmail.com> (raw)
In-Reply-To: <20220510152847.230957-7-hannes@cmpxchg.org>

On Tue, May 10, 2022 at 8:29 AM Johannes Weiner <hannes@cmpxchg.org> wrote:
>
[...]
> +void obj_cgroup_charge_zswap(struct obj_cgroup *objcg, size_t size)
> +{
> +       struct mem_cgroup *memcg;
> +
> +       VM_WARN_ON_ONCE(!(current->flags & PF_MEMALLOC));
> +
> +       /* PF_MEMALLOC context, charging must succeed */
)
Instead of these warnings and comment why not just explicitly use
memalloc_noreclaim_[save|restore]() ?

> +       if (obj_cgroup_charge(objcg, GFP_KERNEL, size))

Can we please make this specific charging an opt-in feature or at
least provide a way to opt-out? This will impact users/providers where
swap is used transparently (in terms of memory usage). Also do you
want this change for v1 users as well?

> +               VM_WARN_ON_ONCE(1);
> +
> +       rcu_read_lock();
> +       memcg = obj_cgroup_memcg(objcg);
> +       mod_memcg_state(memcg, MEMCG_ZSWAP_B, size);
> +       mod_memcg_state(memcg, MEMCG_ZSWAPPED, 1);
> +       rcu_read_unlock();
> +}
> +