Message-ID: <20250910192057.1045711-3-kuniyu@google.com>
Date: Wed, 10 Sep 2025 19:19:29 +0000
From: Kuniyuki Iwashima <kuniyu@...gle.com>
To: Alexei Starovoitov <ast@...nel.org>, Andrii Nakryiko <andrii@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Martin KaFai Lau <martin.lau@...ux.dev>
Cc: John Fastabend <john.fastabend@...il.com>, Stanislav Fomichev <sdf@...ichev.me>, 
	Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...nel.org>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, Shakeel Butt <shakeel.butt@...ux.dev>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Neal Cardwell <ncardwell@...gle.com>, Willem de Bruijn <willemb@...gle.com>, 
	Mina Almasry <almasrymina@...gle.com>, Kuniyuki Iwashima <kuniyu@...gle.com>, 
	Kuniyuki Iwashima <kuni1840@...il.com>, bpf@...r.kernel.org, netdev@...r.kernel.org
Subject: [PATCH v8 bpf-next/net 2/6] net-memcg: Allow decoupling memcg from
 global protocol memory accounting.

Some protocols (e.g., TCP, UDP) implement memory accounting for socket
buffers and charge memory to per-protocol global counters pointed to by
sk->sk_proto->memory_allocated.

If a socket has sk->sk_memcg, this memory is also charged to memcg as
"sock" in memory.stat.

We do not need to pay costs for two orthogonal memory accounting
mechanisms.  A microbenchmark result is in the subsequent bpf patch.

Let's decouple sockets under memcg from the global per-protocol memory
accounting if mem_cgroup_sk_exclusive() returns true.

Note that this does NOT disable memcg, but rather the per-protocol one.

mem_cgroup_sk_exclusive() starts to return true in the following patches,
and then, the per-protocol memory accounting will be skipped.

In __inet_accept(), we need to reclaim counts that are already charged
for child sockets because we do not allocate sk->sk_memcg until accept().

trace_sock_exceed_buf_limit() will always show 0 as accounted for the
memcg-exclusive sockets, but this can be obtained in memory.stat.

Signed-off-by: Kuniyuki Iwashima <kuniyu@...gle.com>
Nacked-by: Johannes Weiner <hannes@...xchg.org>
---
v7: Reorder before sysctl & bpf patches
v6: Update commit message
---
 include/net/proto_memory.h      | 15 ++++++--
 include/net/sock.h              | 10 ++++++
 include/net/tcp.h               | 10 ++++--
 net/core/sock.c                 | 64 ++++++++++++++++++++++-----------
 net/ipv4/af_inet.c              | 12 ++++++-
 net/ipv4/inet_connection_sock.c |  1 +
 net/ipv4/tcp.c                  |  3 +-
 net/ipv4/tcp_output.c           | 10 ++++--
 net/mptcp/protocol.c            |  3 +-
 net/tls/tls_device.c            |  4 ++-
 10 files changed, 100 insertions(+), 32 deletions(-)

diff --git a/include/net/proto_memory.h b/include/net/proto_memory.h
index 72d4ec413ab5..4383cb4cb2d2 100644
--- a/include/net/proto_memory.h
+++ b/include/net/proto_memory.h
@@ -31,13 +31,22 @@ static inline bool sk_under_memory_pressure(const struct sock *sk)
 	if (!sk->sk_prot->memory_pressure)
 		return false;
 
-	if (mem_cgroup_sk_enabled(sk) &&
-	    mem_cgroup_sk_under_memory_pressure(sk))
-		return true;
+	if (mem_cgroup_sk_enabled(sk)) {
+		if (mem_cgroup_sk_under_memory_pressure(sk))
+			return true;
+
+		if (mem_cgroup_sk_exclusive(sk))
+			return false;
+	}
 
 	return !!READ_ONCE(*sk->sk_prot->memory_pressure);
 }
 
+static inline bool sk_should_enter_memory_pressure(struct sock *sk)
+{
+	return !mem_cgroup_sk_enabled(sk) || !mem_cgroup_sk_exclusive(sk);
+}
+
 static inline long
 proto_memory_allocated(const struct proto *prot)
 {
diff --git a/include/net/sock.h b/include/net/sock.h
index 63a6a48afb48..66501ab670eb 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -2607,6 +2607,11 @@ static inline bool mem_cgroup_sk_enabled(const struct sock *sk)
 	return mem_cgroup_sockets_enabled && mem_cgroup_from_sk(sk);
 }
 
+static inline bool mem_cgroup_sk_exclusive(const struct sock *sk)
+{
+	return false;
+}
+
 static inline bool mem_cgroup_sk_under_memory_pressure(const struct sock *sk)
 {
 	struct mem_cgroup *memcg = mem_cgroup_from_sk(sk);
@@ -2634,6 +2639,11 @@ static inline bool mem_cgroup_sk_enabled(const struct sock *sk)
 	return false;
 }
 
+static inline bool mem_cgroup_sk_exclusive(const struct sock *sk)
+{
+	return false;
+}
+
 static inline bool mem_cgroup_sk_under_memory_pressure(const struct sock *sk)
 {
 	return false;
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 2936b8175950..225f6bac06c3 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -275,9 +275,13 @@ extern unsigned long tcp_memory_pressure;
 /* optimized version of sk_under_memory_pressure() for TCP sockets */
 static inline bool tcp_under_memory_pressure(const struct sock *sk)
 {
-	if (mem_cgroup_sk_enabled(sk) &&
-	    mem_cgroup_sk_under_memory_pressure(sk))
-		return true;
+	if (mem_cgroup_sk_enabled(sk)) {
+		if (mem_cgroup_sk_under_memory_pressure(sk))
+			return true;
+
+		if (mem_cgroup_sk_exclusive(sk))
+			return false;
+	}
 
 	return READ_ONCE(tcp_memory_pressure);
 }
diff --git a/net/core/sock.c b/net/core/sock.c
index 8002ac6293dc..814966309b0e 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1046,17 +1046,21 @@ static int sock_reserve_memory(struct sock *sk, int bytes)
 	if (!charged)
 		return -ENOMEM;
 
-	/* pre-charge to forward_alloc */
-	sk_memory_allocated_add(sk, pages);
-	allocated = sk_memory_allocated(sk);
-	/* If the system goes into memory pressure with this
-	 * precharge, give up and return error.
-	 */
-	if (allocated > sk_prot_mem_limits(sk, 1)) {
-		sk_memory_allocated_sub(sk, pages);
-		mem_cgroup_sk_uncharge(sk, pages);
-		return -ENOMEM;
+	if (!mem_cgroup_sk_exclusive(sk)) {
+		/* pre-charge to forward_alloc */
+		sk_memory_allocated_add(sk, pages);
+		allocated = sk_memory_allocated(sk);
+
+		/* If the system goes into memory pressure with this
+		 * precharge, give up and return error.
+		 */
+		if (allocated > sk_prot_mem_limits(sk, 1)) {
+			sk_memory_allocated_sub(sk, pages);
+			mem_cgroup_sk_uncharge(sk, pages);
+			return -ENOMEM;
+		}
 	}
+
 	sk_forward_alloc_add(sk, pages << PAGE_SHIFT);
 
 	WRITE_ONCE(sk->sk_reserved_mem,
@@ -3153,8 +3157,11 @@ bool sk_page_frag_refill(struct sock *sk, struct page_frag *pfrag)
 	if (likely(skb_page_frag_refill(32U, pfrag, sk->sk_allocation)))
 		return true;
 
-	sk_enter_memory_pressure(sk);
+	if (sk_should_enter_memory_pressure(sk))
+		sk_enter_memory_pressure(sk);
+
 	sk_stream_moderate_sndbuf(sk);
+
 	return false;
 }
 EXPORT_SYMBOL(sk_page_frag_refill);
@@ -3267,18 +3274,30 @@ int __sk_mem_raise_allocated(struct sock *sk, int size, int amt, int kind)
 {
 	bool memcg_enabled = false, charged = false;
 	struct proto *prot = sk->sk_prot;
-	long allocated;
-
-	sk_memory_allocated_add(sk, amt);
-	allocated = sk_memory_allocated(sk);
+	long allocated = 0;
 
 	if (mem_cgroup_sk_enabled(sk)) {
+		bool exclusive = mem_cgroup_sk_exclusive(sk);
+
 		memcg_enabled = true;
 		charged = mem_cgroup_sk_charge(sk, amt, gfp_memcg_charge());
-		if (!charged)
+
+		if (exclusive && charged)
+			return 1;
+
+		if (!charged) {
+			if (!exclusive) {
+				sk_memory_allocated_add(sk, amt);
+				allocated = sk_memory_allocated(sk);
+			}
+
 			goto suppress_allocation;
+		}
 	}
 
+	sk_memory_allocated_add(sk, amt);
+	allocated = sk_memory_allocated(sk);
+
 	/* Under limit. */
 	if (allocated <= sk_prot_mem_limits(sk, 0)) {
 		sk_leave_memory_pressure(sk);
@@ -3357,7 +3376,8 @@ int __sk_mem_raise_allocated(struct sock *sk, int size, int amt, int kind)
 
 	trace_sock_exceed_buf_limit(sk, prot, allocated, kind);
 
-	sk_memory_allocated_sub(sk, amt);
+	if (allocated)
+		sk_memory_allocated_sub(sk, amt);
 
 	if (charged)
 		mem_cgroup_sk_uncharge(sk, amt);
@@ -3396,11 +3416,15 @@ EXPORT_SYMBOL(__sk_mem_schedule);
  */
 void __sk_mem_reduce_allocated(struct sock *sk, int amount)
 {
-	sk_memory_allocated_sub(sk, amount);
-
-	if (mem_cgroup_sk_enabled(sk))
+	if (mem_cgroup_sk_enabled(sk)) {
 		mem_cgroup_sk_uncharge(sk, amount);
 
+		if (mem_cgroup_sk_exclusive(sk))
+			return;
+	}
+
+	sk_memory_allocated_sub(sk, amount);
+
 	if (sk_under_global_memory_pressure(sk) &&
 	    (sk_memory_allocated(sk) < sk_prot_mem_limits(sk, 0)))
 		sk_leave_memory_pressure(sk);
diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index d42757f74c6e..52d060bc9009 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -95,6 +95,7 @@
 #include <net/checksum.h>
 #include <net/ip.h>
 #include <net/protocol.h>
+#include <net/proto_memory.h>
 #include <net/arp.h>
 #include <net/route.h>
 #include <net/ip_fib.h>
@@ -769,8 +770,17 @@ void __inet_accept(struct socket *sock, struct socket *newsock, struct sock *new
 			 */
 			amt = sk_mem_pages(newsk->sk_forward_alloc +
 					   atomic_read(&newsk->sk_rmem_alloc));
-			if (amt)
+			if (amt) {
+				/* This amt is already charged globally to
+				 * sk_prot->memory_allocated due to lack of
+				 * sk_memcg until accept(), thus we need to
+				 * reclaim it here if newsk is isolated.
+				 */
+				if (mem_cgroup_sk_exclusive(newsk))
+					sk_memory_allocated_sub(newsk, amt);
+
 				mem_cgroup_sk_charge(newsk, amt, gfp);
+			}
 		}
 
 		kmem_cache_charge(newsk, gfp);
diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index ed10b959a906..f8dd53d40dcf 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -22,6 +22,7 @@
 #include <net/tcp.h>
 #include <net/sock_reuseport.h>
 #include <net/addrconf.h>
+#include <net/proto_memory.h>
 
 #if IS_ENABLED(CONFIG_IPV6)
 /* match_sk*_wildcard == true:  IPV6_ADDR_ANY equals to any IPv6 addresses
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 71a956fbfc55..dcbd49e2f8af 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -908,7 +908,8 @@ struct sk_buff *tcp_stream_alloc_skb(struct sock *sk, gfp_t gfp,
 		}
 		__kfree_skb(skb);
 	} else {
-		sk->sk_prot->enter_memory_pressure(sk);
+		if (sk_should_enter_memory_pressure(sk))
+			tcp_enter_memory_pressure(sk);
 		sk_stream_moderate_sndbuf(sk);
 	}
 	return NULL;
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index dfbac0876d96..4b6a7250a9c2 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -3574,12 +3574,18 @@ void sk_forced_mem_schedule(struct sock *sk, int size)
 	delta = size - sk->sk_forward_alloc;
 	if (delta <= 0)
 		return;
+
 	amt = sk_mem_pages(delta);
 	sk_forward_alloc_add(sk, amt << PAGE_SHIFT);
-	sk_memory_allocated_add(sk, amt);
 
-	if (mem_cgroup_sk_enabled(sk))
+	if (mem_cgroup_sk_enabled(sk)) {
 		mem_cgroup_sk_charge(sk, amt, gfp_memcg_charge() | __GFP_NOFAIL);
+
+		if (mem_cgroup_sk_exclusive(sk))
+			return;
+	}
+
+	sk_memory_allocated_add(sk, amt);
 }
 
 /* Send a FIN. The caller locks the socket for us.
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 9a287b75c1b3..f7487e22a3f8 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -16,6 +16,7 @@
 #include <net/inet_common.h>
 #include <net/inet_hashtables.h>
 #include <net/protocol.h>
+#include <net/proto_memory.h>
 #include <net/tcp_states.h>
 #if IS_ENABLED(CONFIG_MPTCP_IPV6)
 #include <net/transp_v6.h>
@@ -1016,7 +1017,7 @@ static void mptcp_enter_memory_pressure(struct sock *sk)
 	mptcp_for_each_subflow(msk, subflow) {
 		struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
 
-		if (first)
+		if (first && sk_should_enter_memory_pressure(ssk))
 			tcp_enter_memory_pressure(ssk);
 		sk_stream_moderate_sndbuf(ssk);
 
diff --git a/net/tls/tls_device.c b/net/tls/tls_device.c
index f672a62a9a52..6696ef837116 100644
--- a/net/tls/tls_device.c
+++ b/net/tls/tls_device.c
@@ -35,6 +35,7 @@
 #include <linux/netdevice.h>
 #include <net/dst.h>
 #include <net/inet_connection_sock.h>
+#include <net/proto_memory.h>
 #include <net/tcp.h>
 #include <net/tls.h>
 #include <linux/skbuff_ref.h>
@@ -371,7 +372,8 @@ static int tls_do_allocation(struct sock *sk,
 	if (!offload_ctx->open_record) {
 		if (unlikely(!skb_page_frag_refill(prepend_size, pfrag,
 						   sk->sk_allocation))) {
-			READ_ONCE(sk->sk_prot)->enter_memory_pressure(sk);
+			if (sk_should_enter_memory_pressure(sk))
+				READ_ONCE(sk->sk_prot)->enter_memory_pressure(sk);
 			sk_stream_moderate_sndbuf(sk);
 			return -ENOMEM;
 		}
-- 
2.51.0.384.g4c02a37b29-goog

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