Patch "net/dst: use a smaller percpu_counter batch for dst entries accounting" has been added to the 4.19-stable tree

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This is a note to let you know that I've just added the patch titled

    net/dst: use a smaller percpu_counter batch for dst entries accounting

to the 4.19-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     net-dst-use-a-smaller-percpu_counter-batch-for-dst-entries-accounting.patch
and it can be found in the queue-4.19 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.


>From SRS0=s4sW=IX=amazon.com=prvs=73518ea15=surajjs@xxxxxxxxxx Sat Jan 13 01:55:35 2024
From: Suraj Jitindar Singh <surajjs@xxxxxxxxxx>
Date: Fri, 12 Jan 2024 16:53:06 -0800
Subject: net/dst: use a smaller percpu_counter batch for dst entries accounting
To: <stable@xxxxxxxxxxxxxxx>
Cc: <gregkh@xxxxxxxxxxxxxxxxxxx>, <trawets@xxxxxxxxxx>, <security@xxxxxxxxxx>, Eric Dumazet <edumazet@xxxxxxxxxx>, Jakub Kicinski <kuba@xxxxxxxxxx>, "Suraj Jitindar Singh" <surajjs@xxxxxxxxxx>
Message-ID: <20240113005308.2422331-2-surajjs@xxxxxxxxxx>

From: Eric Dumazet <edumazet@xxxxxxxxxx>

commit cf86a086a18095e33e0637cb78cda1fcf5280852 upstream.

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@xxxxxxxxxx>
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Suraj Jitindar Singh <surajjs@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # 4.19.x
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 include/net/dst_ops.h |    4 +++-
 net/core/dst.c        |    8 ++++----
 net/ipv6/route.c      |    3 +++
 3 files changed, 10 insertions(+), 5 deletions(-)

--- a/include/net/dst_ops.h
+++ b/include/net/dst_ops.h
@@ -53,9 +53,11 @@ static inline int dst_entries_get_slow(s
 	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)
--- a/net/core/dst.c
+++ b/net/core/dst.c
@@ -97,11 +97,11 @@ void *dst_alloc(struct dst_ops *ops, str
 {
 	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;
 		}
 	}
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -2778,6 +2778,9 @@ static int ip6_dst_gc(struct dst_ops *op
 	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;


Patches currently in stable-queue which might be from surajjs@xxxxxxxxxx are

queue-4.19/ipv6-remove-max_size-check-inline-with-ipv4.patch
queue-4.19/net-dst-use-a-smaller-percpu_counter-batch-for-dst-entries-accounting.patch
queue-4.19/net-add-a-route-cache-full-diagnostic-message.patch




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