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From:   Abel Wu <wuyun.abel@bytedance.com>
To:     "David S . Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>
Cc:     netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        Abel Wu <wuyun.abel@bytedance.com>
Subject: [PATCH] sock: Fix misuse of sk_under_memory_pressure()
Date:   Sat,  6 May 2023 16:59:03 +0800
Message-Id: <20230506085903.96133-1-wuyun.abel@bytedance.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

The commit 180d8cd942ce ("foundations of per-cgroup memory pressure
controlling") wrapped proto::memory_pressure status into an accessor
named sk_under_memory_pressure(), and in the next commit e1aab161e013
("socket: initial cgroup code") added the consideration of net-memcg
pressure into this accessor.

But with the former patch applied, not all of the call sites of
sk_under_memory_pressure() are interested in net-memcg's pressure.
The __sk_mem_{raise,reduce}_allocated() only focus on proto/netns
pressure rather than net-memcg's. IOW this accessor are generally
used for deciding whether should reclaim or not.

Fixes: e1aab161e013 ("socket: initial cgroup code")
Signed-off-by: Abel Wu <wuyun.abel@bytedance.com>
---
 include/net/sock.h |  5 -----
 net/core/sock.c    | 17 +++++++++--------
 2 files changed, 9 insertions(+), 13 deletions(-)

diff --git a/include/net/sock.h b/include/net/sock.h
index 8b7ed7167243..752d51030c5a 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1404,11 +1404,6 @@ static inline int sk_under_cgroup_hierarchy(struct sock *sk,
 #endif
 }
 
-static inline bool sk_has_memory_pressure(const struct sock *sk)
-{
-	return sk->sk_prot->memory_pressure != NULL;
-}
-
 static inline bool sk_under_memory_pressure(const struct sock *sk)
 {
 	if (!sk->sk_prot->memory_pressure)
diff --git a/net/core/sock.c b/net/core/sock.c
index 5440e67bcfe3..8d215f821ea6 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -3017,13 +3017,14 @@ int __sk_mem_raise_allocated(struct sock *sk, int size, int amt, int kind)
 		}
 	}
 
-	if (sk_has_memory_pressure(sk)) {
-		u64 alloc;
-
-		if (!sk_under_memory_pressure(sk))
-			return 1;
-		alloc = sk_sockets_allocated_read_positive(sk);
-		if (sk_prot_mem_limits(sk, 2) > alloc *
+	if (prot->memory_pressure) {
+		/*
+		 * If under global pressure, allow the sockets that are below
+		 * average memory usage to raise, trying to be fair between all
+		 * the sockets under global constrains.
+		 */
+		if (!*prot->memory_pressure ||
+		    sk_prot_mem_limits(sk, 2) > sk_sockets_allocated_read_positive(sk) *
 		    sk_mem_pages(sk->sk_wmem_queued +
 				 atomic_read(&sk->sk_rmem_alloc) +
 				 sk->sk_forward_alloc))
@@ -3095,7 +3096,7 @@ void __sk_mem_reduce_allocated(struct sock *sk, int amount)
 	if (mem_cgroup_sockets_enabled && sk->sk_memcg)
 		mem_cgroup_uncharge_skmem(sk->sk_memcg, amount);
 
-	if (sk_under_memory_pressure(sk) &&
+	if (sk->sk_prot->memory_pressure && *sk->sk_prot->memory_pressure &&
 	    (sk_memory_allocated(sk) < sk_prot_mem_limits(sk, 0)))
 		sk_leave_memory_pressure(sk);
 }
-- 
2.37.3