netdev - [PATCH 4/8] net: tcp_memcontrol: remove bogus hierarchy pressure propagation

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Date:	Wed,  4 Nov 2015 17:22:10 -0500
From:	Johannes Weiner <hannes@...xchg.org>
To:	David Miller <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Michal Hocko <mhocko@...e.cz>,
	Vladimir Davydov <vdavydov@...tuozzo.com>,
	Tejun Heo <tj@...nel.org>, netdev@...r.kernel.org,
	linux-mm@...ck.org, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org, kernel-team@...com
Subject: [PATCH 4/8] net: tcp_memcontrol: remove bogus hierarchy pressure propagation

When a cgroup currently breaches its socket memory limit, it enters
memory pressure mode for itself and its *parents*. This throttles
transmission in unrelated groups that have nothing to do with the
breached limit.

On the contrary, breaching a limit should make that group and its
*children* enter memory pressure mode. But this happens already,
albeit lazily: if a parent limit is breached, siblings will enter
memory pressure on their own once the next packet arrives for them.

So no additional hierarchy code is needed. Remove the bogus stuff.

Signed-off-by: Johannes Weiner <hannes@...xchg.org>
---
 include/net/sock.h | 19 ++++---------------
 1 file changed, 4 insertions(+), 15 deletions(-)

diff --git a/include/net/sock.h b/include/net/sock.h
index 59a7196..d541bed 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1152,14 +1152,8 @@ static inline void sk_leave_memory_pressure(struct sock *sk)
 	if (*memory_pressure)
 		*memory_pressure = 0;
 
-	if (mem_cgroup_sockets_enabled && sk->sk_cgrp) {
-		struct cg_proto *cg_proto = sk->sk_cgrp;
-		struct proto *prot = sk->sk_prot;
-
-		for (; cg_proto; cg_proto = parent_cg_proto(prot, cg_proto))
-			cg_proto->memory_pressure = 0;
-	}
-
+	if (mem_cgroup_sockets_enabled && sk->sk_cgrp)
+		sk->sk_cgrp->memory_pressure = 0;
 }
 
 static inline void sk_enter_memory_pressure(struct sock *sk)
@@ -1167,13 +1161,8 @@ static inline void sk_enter_memory_pressure(struct sock *sk)
 	if (!sk->sk_prot->enter_memory_pressure)
 		return;
 
-	if (mem_cgroup_sockets_enabled && sk->sk_cgrp) {
-		struct cg_proto *cg_proto = sk->sk_cgrp;
-		struct proto *prot = sk->sk_prot;
-
-		for (; cg_proto; cg_proto = parent_cg_proto(prot, cg_proto))
-			cg_proto->memory_pressure = 1;
-	}
+	if (mem_cgroup_sockets_enabled && sk->sk_cgrp)
+		sk->sk_cgrp->memory_pressure = 1;
 
 	sk->sk_prot->enter_memory_pressure(sk);
 }
-- 
2.6.2

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