netdev - [PATCH net-next] net/sched: get rid of qdisc->padded

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Message-Id: <20201007165111.172419-1-eric.dumazet@gmail.com>
Date:   Wed,  7 Oct 2020 09:51:11 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     "David S . Miller" <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Allen Pais <allen.lkml@...il.com>
Subject: [PATCH net-next] net/sched: get rid of qdisc->padded

From: Eric Dumazet <edumazet@...gle.com>

kmalloc() of sufficiently big portion of memory is cache-aligned
in regular conditions. If some debugging options are used,
there is no reason qdisc structures would need 64-byte alignment
if most other kernel structures are not aligned.

This get rid of QDISC_ALIGN and QDISC_ALIGNTO.

Addition of privdata field will help implementing
the reverse of qdisc_priv() and documents where
the private data is.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Cong Wang <xiyou.wangcong@...il.com>
Cc: Allen Pais <allen.lkml@...il.com>
---
 include/net/pkt_sched.h   |  5 +----
 include/net/sch_generic.h |  5 ++++-
 net/sched/sch_generic.c   | 23 +++++------------------
 3 files changed, 10 insertions(+), 23 deletions(-)

diff --git a/include/net/pkt_sched.h b/include/net/pkt_sched.h
index ac8c890a2657e35546ec51fe8b8a993a2bd0c91b..4ed32e6b020145afb015c3c07d2ec3a613f1311d 100644
--- a/include/net/pkt_sched.h
+++ b/include/net/pkt_sched.h
@@ -19,12 +19,9 @@ struct qdisc_walker {
 	int	(*fn)(struct Qdisc *, unsigned long cl, struct qdisc_walker *);
 };
 
-#define QDISC_ALIGNTO		64
-#define QDISC_ALIGN(len)	(((len) + QDISC_ALIGNTO-1) & ~(QDISC_ALIGNTO-1))
-
 static inline void *qdisc_priv(struct Qdisc *q)
 {
-	return (char *) q + QDISC_ALIGN(sizeof(struct Qdisc));
+	return &q->privdata;
 }
 
 /* 
diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index 6c762457122fd0091cb0f2bf41bda73babc4ac12..d8fd8676fc724110630904909f64d7789f3a4b47 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -91,7 +91,7 @@ struct Qdisc {
 	struct net_rate_estimator __rcu *rate_est;
 	struct gnet_stats_basic_cpu __percpu *cpu_bstats;
 	struct gnet_stats_queue	__percpu *cpu_qstats;
-	int			padded;
+	int			pad;
 	refcount_t		refcnt;
 
 	/*
@@ -112,6 +112,9 @@ struct Qdisc {
 	/* for NOLOCK qdisc, true if there are no enqueued skbs */
 	bool			empty;
 	struct rcu_head		rcu;
+
+	/* private data */
+	long privdata[] ____cacheline_aligned;
 };
 
 static inline void qdisc_refcount_inc(struct Qdisc *qdisc)
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 54c417244642a1445c618e6adf0e38b2d4f84565..49eae93d1489dc3513b41c237ca3f572e21ff203 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -802,9 +802,8 @@ struct Qdisc *qdisc_alloc(struct netdev_queue *dev_queue,
 			  const struct Qdisc_ops *ops,
 			  struct netlink_ext_ack *extack)
 {
-	void *p;
 	struct Qdisc *sch;
-	unsigned int size = QDISC_ALIGN(sizeof(*sch)) + ops->priv_size;
+	unsigned int size = sizeof(*sch) + ops->priv_size;
 	int err = -ENOBUFS;
 	struct net_device *dev;
 
@@ -815,22 +814,10 @@ struct Qdisc *qdisc_alloc(struct netdev_queue *dev_queue,
 	}
 
 	dev = dev_queue->dev;
-	p = kzalloc_node(size, GFP_KERNEL,
-			 netdev_queue_numa_node_read(dev_queue));
+	sch = kzalloc_node(size, GFP_KERNEL, netdev_queue_numa_node_read(dev_queue));
 
-	if (!p)
+	if (!sch)
 		goto errout;
-	sch = (struct Qdisc *) QDISC_ALIGN((unsigned long) p);
-	/* if we got non aligned memory, ask more and do alignment ourself */
-	if (sch != p) {
-		kfree(p);
-		p = kzalloc_node(size + QDISC_ALIGNTO - 1, GFP_KERNEL,
-				 netdev_queue_numa_node_read(dev_queue));
-		if (!p)
-			goto errout;
-		sch = (struct Qdisc *) QDISC_ALIGN((unsigned long) p);
-		sch->padded = (char *) sch - (char *) p;
-	}
 	__skb_queue_head_init(&sch->gso_skb);
 	__skb_queue_head_init(&sch->skb_bad_txq);
 	qdisc_skb_head_init(&sch->q);
@@ -873,7 +860,7 @@ struct Qdisc *qdisc_alloc(struct netdev_queue *dev_queue,
 
 	return sch;
 errout1:
-	kfree(p);
+	kfree(sch);
 errout:
 	return ERR_PTR(err);
 }
@@ -941,7 +928,7 @@ void qdisc_free(struct Qdisc *qdisc)
 		free_percpu(qdisc->cpu_qstats);
 	}
 
-	kfree((char *) qdisc - qdisc->padded);
+	kfree(qdisc);
 }
 
 static void qdisc_free_cb(struct rcu_head *head)
-- 
2.28.0.806.g8561365e88-goog