netdev - [PATCH net-next] net: shrink napi_skb_cache

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Message-ID: <20251015233801.2977044-1-edumazet@google.com>
Date: Wed, 15 Oct 2025 23:38:01 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: Simon Horman <horms@...nel.org>, Kuniyuki Iwashima <kuniyu@...gle.com>, netdev@...r.kernel.org, 
	eric.dumazet@...il.com, Eric Dumazet <edumazet@...gle.com>, 
	Alexander Lobakin <aleksander.lobakin@...el.com>
Subject: [PATCH net-next] net: shrink napi_skb_cache_put()

Following loop in napi_skb_cache_put() is unrolled by the compiler
even if CONFIG_KASAN is not enabled:

for (i = NAPI_SKB_CACHE_HALF; i < NAPI_SKB_CACHE_SIZE; i++)
	kasan_mempool_unpoison_object(nc->skb_cache[i],
				kmem_cache_size(net_hotdata.skbuff_cache));

We have 32 times this sequence, for a total of 384 bytes.

	48 8b 3d 00 00 00 00 	net_hotdata.skbuff_cache,%rdi
	e8 00 00 00 00       	call   kmem_cache_size

This is because kmem_cache_size() is an extern function,
and kasan_unpoison_object_data() is an inline function.

Cache kmem_cache_size() result in a temporary variable, and
make the loop conditional to CONFIG_KASAN.

After this patch, napi_skb_cache_put() is inlined in its callers.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Alexander Lobakin <aleksander.lobakin@...el.com>
---
 net/core/skbuff.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index bc12790017b0b5c0be99f8fb9d362b3730fa4eb0..5a8b48b201843f94b5fdaab3241801f642fbd1f0 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -1426,10 +1426,13 @@ static void napi_skb_cache_put(struct sk_buff *skb)
 	nc->skb_cache[nc->skb_count++] = skb;
 
 	if (unlikely(nc->skb_count == NAPI_SKB_CACHE_SIZE)) {
-		for (i = NAPI_SKB_CACHE_HALF; i < NAPI_SKB_CACHE_SIZE; i++)
-			kasan_mempool_unpoison_object(nc->skb_cache[i],
-						kmem_cache_size(net_hotdata.skbuff_cache));
+		if (IS_ENABLED(CONFIG_KASAN)) {
+			u32 size = kmem_cache_size(net_hotdata.skbuff_cache);
 
+			for (i = NAPI_SKB_CACHE_HALF; i < NAPI_SKB_CACHE_SIZE; i++)
+				kasan_mempool_unpoison_object(nc->skb_cache[i],
+							      size);
+		}
 		kmem_cache_free_bulk(net_hotdata.skbuff_cache, NAPI_SKB_CACHE_HALF,
 				     nc->skb_cache + NAPI_SKB_CACHE_HALF);
 		nc->skb_count = NAPI_SKB_CACHE_HALF;
-- 
2.51.0.869.ge66316f041-goog