linux-kernel - [PATCH net] net: gro: flush the real oldest skb

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Date:   Wed, 27 Oct 2021 16:49:44 +0800
From:   kerneljasonxing@...il.com
To:     davem@...emloft.net, kuba@...nel.org, ast@...nel.org,
        daniel@...earbox.net, hawk@...nel.org, john.fastabend@...il.com,
        andrii@...nel.org, kafai@...com, songliubraving@...com, yhs@...com,
        kpsingh@...nel.org, edumazet@...gle.com, atenart@...nel.org,
        alobakin@...me, weiwan@...gle.com, bjorn@...nel.org, arnd@...db.de,
        memxor@...il.com
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org, kerneljasonxing@...il.com,
        Jason Xing <xingwanli@...ishou.com>
Subject: [PATCH net] net: gro: flush the real oldest skb

From: Jason Xing <xingwanli@...ishou.com>

Prior to this patch, when the count of skbs of one flow is larger than
MAX_GRO_SKBS, gro_flush_oldest() flushes the tail of the list. However,
as we can see in the merge part of skb_gro_receive(), the tail of the
list is the newest, head oldest.

Here, we need to fetch the real oldest one and then process it to lower
the latency.

Fix: 07d78363dc ("net: Convert NAPI gro list into a small hash table.")
Signed-off-by: Jason Xing <xingwanli@...ishou.com>
---
 net/core/dev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 7ee9fec..d52ebdb 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6012,7 +6012,7 @@ static void gro_flush_oldest(struct napi_struct *napi, struct list_head *head)
 {
 	struct sk_buff *oldest;
 
-	oldest = list_last_entry(head, struct sk_buff, list);
+	oldest = list_first_entry(head, struct sk_buff, list);
 
 	/* We are called with head length >= MAX_GRO_SKBS, so this is
 	 * impossible.
-- 
1.8.3.1