[PATCH net-next 3/4] net: use NAPI_SKB_CACHE_FREE to keep 32 as default to do bulk free

[Jason Xing <kerneljasonxing@gmail.com>]

From: Jason Xing <kernelxing@tencent.com>

- Replace NAPI_SKB_CACHE_HALF with NAPI_SKB_CACHE_FREE
- Only free 32 skbs in napi_skb_cache_put()

Since the first patch adjusting NAPI_SKB_CACHE_SIZE to 128, the number
of packets to be freed in the softirq was increased from 32 to 64.
Considering a subsequent net_rx_action() calling napi_poll() a few
times can easily consume the 64 available slots and we can afford
keeping a higher value of sk_buffs in per-cpu storage, decrease
NAPI_SKB_CACHE_FREE to 32 like before. So now the logic is 1) keeping
96 skbs, 2) freeing 32 skbs at one time.

Suggested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Jason Xing <kernelxing@tencent.com>
---
 net/core/skbuff.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index b6fe7ab85c4a..d81ac78c32ff 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -225,7 +225,7 @@ static void skb_under_panic(struct sk_buff *skb, unsigned int sz, void *addr)
 
 #define NAPI_SKB_CACHE_SIZE	128
 #define NAPI_SKB_CACHE_BULK	32
-#define NAPI_SKB_CACHE_HALF	(NAPI_SKB_CACHE_SIZE / 2)
+#define NAPI_SKB_CACHE_FREE	32
 
 struct napi_alloc_cache {
 	local_lock_t bh_lock;
@@ -1445,7 +1445,6 @@ void __consume_stateless_skb(struct sk_buff *skb)
 static void napi_skb_cache_put(struct sk_buff *skb)
 {
 	struct napi_alloc_cache *nc = this_cpu_ptr(&napi_alloc_cache);
-	u32 i;
 
 	if (!kasan_mempool_poison_object(skb))
 		return;
@@ -1454,13 +1453,16 @@ 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++)
+		u32 i, remaining = NAPI_SKB_CACHE_SIZE - NAPI_SKB_CACHE_FREE;
+
+		for (i = remaining; i < NAPI_SKB_CACHE_SIZE; i++)
 			kasan_mempool_unpoison_object(nc->skb_cache[i],
 						skbuff_cache_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;
+		kmem_cache_free_bulk(net_hotdata.skbuff_cache,
+				     NAPI_SKB_CACHE_FREE,
+				     nc->skb_cache + remaining);
+		nc->skb_count = remaining;
 	}
 	local_unlock_nested_bh(&napi_alloc_cache.bh_lock);
 }
-- 
2.41.3