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[82.132.233.133]) by smtp.gmail.com with ESMTPSA id c12-20020a05600c0a4c00b00381141f4967sm7866995wmq.35.2022.04.03.06.08.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 03 Apr 2022 06:08:12 -0700 (PDT) From: Pavel Begunkov To: netdev@vger.kernel.org, "David S . Miller" , Jakub Kicinski Cc: Eric Dumazet , Wei Liu , Paul Durrant , Pavel Begunkov Subject: [PATCH net-next 02/27] sock: optimise sock_def_write_space send refcounting Date: Sun, 3 Apr 2022 14:06:14 +0100 Message-Id: <769468f1e09dc13caefaa5cebc3ed1e04f747bcc.1648981570.git.asml.silence@gmail.com> X-Mailer: git-send-email 2.35.1 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org sock_def_write_space() is extensively used by UDP and there is some room for optimisation. When sock_wfree() needs to do ->sk_write_space(), it modifies ->sk_wmem_alloc in two steps. First, it puts all but one refs and calls ->sk_write_space(), and then puts down remaining 1. That's needed because the callback relies on ->sk_wmem_alloc being subbed but something should hold the socket alive. The idea behind this patch is to take advantage of SOCK_RCU_FREE and ensure the socket is not freed by wrapping ->sk_write_space() in an RCU section. Then we can remove one extra refcount atomic. Note: not all callbacks might be RCU prepared, so we carve out a sock_def_write_space() specific path. Signed-off-by: Pavel Begunkov --- net/core/sock.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/net/core/sock.c b/net/core/sock.c index f5766d6e27cb..9389bb602c64 100644 --- a/net/core/sock.c +++ b/net/core/sock.c @@ -144,6 +144,8 @@ static DEFINE_MUTEX(proto_list_mutex); static LIST_HEAD(proto_list); +static void sock_def_write_space(struct sock *sk); + /** * sk_ns_capable - General socket capability test * @sk: Socket to use a capability on or through @@ -2300,8 +2302,20 @@ void sock_wfree(struct sk_buff *skb) { struct sock *sk = skb->sk; unsigned int len = skb->truesize; + bool free; if (!sock_flag(sk, SOCK_USE_WRITE_QUEUE)) { + if (sock_flag(sk, SOCK_RCU_FREE) && + sk->sk_write_space == sock_def_write_space) { + rcu_read_lock(); + free = refcount_sub_and_test(len, &sk->sk_wmem_alloc); + sock_def_write_space(sk); + rcu_read_unlock(); + if (unlikely(free)) + __sk_free(sk); + return; + } + /* * Keep a reference on sk_wmem_alloc, this will be released * after sk_write_space() call -- 2.35.1