[PATCH v4 1/4] net-memcg: Fold dependency into memcg pressure cond

[Abel Wu]

The callers of mem_cgroup_under_socket_pressure() should always make
sure that (mem_cgroup_sockets_enabled && sk->sk_memcg) is true. So
instead of coding around all the callsites, put the dependencies into
mem_cgroup_under_socket_pressure() to avoid redundancy and possibly
bugs.

This change might also introduce slight function call overhead *iff*
the function gets expanded in the future. But for now this change
doesn't make binaries different (checked by vimdiff) except the one
net/ipv4/tcp_input.o (by scripts/bloat-o-meter), which is probably
negligible to performance:

add/remove: 0/0 grow/shrink: 1/2 up/down: 5/-5 (0)
Function                                     old     new   delta
tcp_grow_window                              573     578      +5
tcp_try_rmem_schedule                       1083    1081      -2
tcp_check_space                              324     321      -3
Total: Before=44647, After=44647, chg +0.00%

So folding the dependencies into mem_cgroup_under_socket_pressure()
is generally a good thing and provides better readablility.

Signed-off-by: Abel Wu <wuyun.abel@xxxxxxxxxxxxx>
---
 include/linux/memcontrol.h | 2 ++
 include/net/sock.h         | 3 +--
 include/net/tcp.h          | 3 +--
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 222d7370134c..a1aead140ff8 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -1743,6 +1743,8 @@ void mem_cgroup_sk_alloc(struct sock *sk);
 void mem_cgroup_sk_free(struct sock *sk);
 static inline bool mem_cgroup_under_socket_pressure(struct mem_cgroup *memcg)
 {
+	if (!mem_cgroup_sockets_enabled || !memcg)
+		return false;
 	if (!cgroup_subsys_on_dfl(memory_cgrp_subsys) && memcg->tcpmem_pressure)
 		return true;
 	do {
diff --git a/include/net/sock.h b/include/net/sock.h
index 8b7ed7167243..641c9373b44b 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1414,8 +1414,7 @@ static inline bool sk_under_memory_pressure(const struct sock *sk)
 	if (!sk->sk_prot->memory_pressure)
 		return false;
 
-	if (mem_cgroup_sockets_enabled && sk->sk_memcg &&
-	    mem_cgroup_under_socket_pressure(sk->sk_memcg))
+	if (mem_cgroup_under_socket_pressure(sk->sk_memcg))
 		return true;
 
 	return !!*sk->sk_prot->memory_pressure;
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 04a31643cda3..3c5e3718b454 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -261,8 +261,7 @@ 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_sockets_enabled && sk->sk_memcg &&
-	    mem_cgroup_under_socket_pressure(sk->sk_memcg))
+	if (mem_cgroup_under_socket_pressure(sk->sk_memcg))
 		return true;
 
 	return READ_ONCE(tcp_memory_pressure);
-- 
2.37.3