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From: Shakeel Butt To: Kuniyuki Iwashima Cc: "David S. Miller" , Eric Dumazet , Jakub Kicinski , Neal Cardwell , Paolo Abeni , Willem de Bruijn , Matthieu Baerts , Mat Martineau , Johannes Weiner , Michal Hocko , Roman Gushchin , Andrew Morton , Michal =?utf-8?Q?Koutn=C3=BD?= , Tejun Heo , Simon Horman , Geliang Tang , Muchun Song , Mina Almasry , Kuniyuki Iwashima , netdev@vger.kernel.org, mptcp@lists.linux.dev, cgroups@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v4 net-next 01/10] mptcp: Fix up subflow's memcg when CONFIG_SOCK_CGROUP_DATA=n. Message-ID: References: <20250814200912.1040628-1-kuniyu@google.com> <20250814200912.1040628-2-kuniyu@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: D2347180009 X-Stat-Signature: aac5r879nc3y8myzkrubttrg9n9hosx3 X-HE-Tag: 1755219963-239934 X-HE-Meta: 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 xeHxbjHL yuQ0hnL4JNBd4aa16lPNroaasOSpTVOTlCKQxEiRVdFJpoHvmx5/88iHoLw5uVGPMKPBivIcBG3juey4OyBnAr7vRz42fzrtp7l8Oi5O7DTYR9Bf0ruDdur/XeEueWxw2pzBuJzeBpT6iyteNr2YrR8uMs7C2IK0L/RpABIIunl+dFb4PKChZeiKcXf+ByfCY7r3OiAsVv7y+sldlrnToj+yEfhxFd/NceOsYtvwkhzVWH5cZKiQX1lNQ5n+slcNboJrcwR7RBLjOFNgd5CCANW79lyIcFtVVNzhbyVIB+QGYzDnFS9xjjMJN/TG5te7hRTDnQo9Fy7twHsNtypTauujIu0lBl7QkTi9C8Qju9RRji8Y= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Aug 14, 2025 at 05:05:56PM -0700, Kuniyuki Iwashima wrote: > On Thu, Aug 14, 2025 at 4:46 PM Shakeel Butt wrote: > > > > On Thu, Aug 14, 2025 at 04:27:31PM -0700, Kuniyuki Iwashima wrote: > > > On Thu, Aug 14, 2025 at 2:44 PM Shakeel Butt wrote: > > > > > > > > On Thu, Aug 14, 2025 at 08:08:33PM +0000, Kuniyuki Iwashima wrote: > > > > > When sk_alloc() allocates a socket, mem_cgroup_sk_alloc() sets > > > > > sk->sk_memcg based on the current task. > > > > > > > > > > MPTCP subflow socket creation is triggered from userspace or > > > > > an in-kernel worker. > > > > > > > > > > In the latter case, sk->sk_memcg is not what we want. So, we fix > > > > > it up from the parent socket's sk->sk_memcg in mptcp_attach_cgroup(). > > > > > > > > > > Although the code is placed under #ifdef CONFIG_MEMCG, it is buried > > > > > under #ifdef CONFIG_SOCK_CGROUP_DATA. > > > > > > > > > > The two configs are orthogonal. If CONFIG_MEMCG is enabled without > > > > > CONFIG_SOCK_CGROUP_DATA, the subflow's memory usage is not charged > > > > > correctly. > > > > > > > > > > Let's wrap sock_create_kern() for subflow with set_active_memcg() > > > > > using the parent sk->sk_memcg. > > > > > > > > > > Fixes: 3764b0c5651e3 ("mptcp: attach subflow socket to parent cgroup") > > > > > Suggested-by: Michal Koutný > > > > > Signed-off-by: Kuniyuki Iwashima > > > > > --- > > > > > mm/memcontrol.c | 5 ++++- > > > > > net/mptcp/subflow.c | 11 +++-------- > > > > > 2 files changed, 7 insertions(+), 9 deletions(-) > > > > > > > > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > > > > > index 8dd7fbed5a94..450862e7fd7a 100644 > > > > > --- a/mm/memcontrol.c > > > > > +++ b/mm/memcontrol.c > > > > > @@ -5006,8 +5006,11 @@ void mem_cgroup_sk_alloc(struct sock *sk) > > > > > if (!in_task()) > > > > > return; > > > > > > > > > > + memcg = current->active_memcg; > > > > > + > > > > > > > > Use active_memcg() instead of current->active_memcg and do before the > > > > !in_task() check. > > > > > > Why not reuse the !in_task() check here ? > > > We never use int_active_memcg for socket and also > > > know int_active_memcg is always NULL here. > > > > > > > If we are making mem_cgroup_sk_alloc() work with set_active_memcg() > > infra then make it work for both in_task() and !in_task() contexts. > > Considering e876ecc67db80, then I think we should add > set_active_memcg_in_task() and active_memcg_in_task(). > > or at least we need WARN_ON() if we want to place active_memcg() > before the in_task() check, but this looks ugly. > > memcg = active_memcg(); > if (!in_task() && !memcg) > return; > DEBUG_NET_WARN_ON_ONCE(!in_task() && memcg)) You don't have to use the code as is. It is just an example. Basically I am asking if in future someone does the following: // in !in_task() context old_memcg = set_active_memcg(new_memcg); sk = sk_alloc(); set_active_memcg(old_memcg); mem_cgroup_sk_alloc() should work and associate the sk with the new_memcg. You can manually inline active_memcg() function to avoid multiple in_task() checks like below: void mem_cgroup_sk_alloc(struct sock *sk) { struct mem_cgroup *memcg; if (!mem_cgroup_sockets_enabled) return; if (!in_task()) { memcg = this_cpu_read(int_active_memcg); /* * Do not associate the sock with unrelated interrupted * task's memcg. */ if (!memcg) return; } else { memcg = current->active_memcg; } rcu_read_lock(); if (likely(!memcg)) memcg = mem_cgroup_from_task(current); if (mem_cgroup_is_root(memcg)) goto out; if (!cgroup_subsys_on_dfl(memory_cgrp_subsys) && !memcg1_tcpmem_active(memcg)) goto out; if (css_tryget(&memcg->css)) sk->sk_memcg = memcg; out: rcu_read_unlock(); }