netdev - [PATCH net-next] net/dst: use a smaller percpu_counter batch for dst entries accounting

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Date:   Thu,  7 May 2020 18:58:10 -0700
From:   Eric Dumazet <edumazet@...gle.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>
Subject: [PATCH net-next] net/dst: use a smaller percpu_counter batch for dst
 entries accounting

percpu_counter_add() uses a default batch size which is quite big
on platforms with 256 cpus. (2*256 -> 512)

This means dst_entries_get_fast() can be off by +/- 2*(nr_cpus^2)
(131072 on servers with 256 cpus)

Reduce the batch size to something more reasonable, and
add logic to ip6_dst_gc() to call dst_entries_get_slow()
before calling the _very_ expensive fib6_run_gc() function.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 include/net/dst_ops.h | 4 +++-
 net/core/dst.c        | 8 ++++----
 net/ipv6/route.c      | 3 +++
 3 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/include/net/dst_ops.h b/include/net/dst_ops.h
index 443863c7b8da362476c15fd290ac2a32a8aa86e3..88ff7bb2bb9bd950cc54fd5e0ae4573d4c66873d 100644
--- a/include/net/dst_ops.h
+++ b/include/net/dst_ops.h
@@ -53,9 +53,11 @@ static inline int dst_entries_get_slow(struct dst_ops *dst)
 	return percpu_counter_sum_positive(&dst->pcpuc_entries);
 }
 
+#define DST_PERCPU_COUNTER_BATCH 32
 static inline void dst_entries_add(struct dst_ops *dst, int val)
 {
-	percpu_counter_add(&dst->pcpuc_entries, val);
+	percpu_counter_add_batch(&dst->pcpuc_entries, val,
+				 DST_PERCPU_COUNTER_BATCH);
 }
 
 static inline int dst_entries_init(struct dst_ops *dst)
diff --git a/net/core/dst.c b/net/core/dst.c
index 193af526e908afa4b868cf128470f0fbc3850698..d6b6ced0d451a39c0ccb88ae39dba225ea9f5705 100644
--- a/net/core/dst.c
+++ b/net/core/dst.c
@@ -81,11 +81,11 @@ void *dst_alloc(struct dst_ops *ops, struct net_device *dev,
 {
 	struct dst_entry *dst;
 
-	if (ops->gc && dst_entries_get_fast(ops) > ops->gc_thresh) {
+	if (ops->gc &&
+	    !(flags & DST_NOCOUNT) &&
+	    dst_entries_get_fast(ops) > ops->gc_thresh) {
 		if (ops->gc(ops)) {
-			printk_ratelimited(KERN_NOTICE "Route cache is full: "
-					   "consider increasing sysctl "
-					   "net.ipv[4|6].route.max_size.\n");
+			pr_notice_ratelimited("Route cache is full: consider increasing sysctl net.ipv6.route.max_size.\n");
 			return NULL;
 		}
 	}
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 1ff142393c768f85c495474a1d05e1ae1642301c..a9072dba00f4fb0b61bce1fc0f44a3a81ba702fa 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -3195,6 +3195,9 @@ static int ip6_dst_gc(struct dst_ops *ops)
 	int entries;
 
 	entries = dst_entries_get_fast(ops);
+	if (entries > rt_max_size)
+		entries = dst_entries_get_slow(ops);
+
 	if (time_after(rt_last_gc + rt_min_interval, jiffies) &&
 	    entries <= rt_max_size)
 		goto out;
-- 
2.26.2.645.ge9eca65c58-goog