linux-kernel - [PATCH net] skbuff: back tiny skbs with kmalloc() in __netdev_alloc

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Message-ID: <20210114235423.232737-1-alobakin@pm.me>
Date:   Thu, 14 Jan 2021 23:54:55 +0000
From:   Alexander Lobakin <alobakin@...me>
To:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     Willem de Bruijn <willemb@...gle.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Alexander Lobakin <alobakin@...me>,
        Guillaume Nault <gnault@...hat.com>,
        Yunsheng Lin <linyunsheng@...wei.com>,
        Florian Westphal <fw@...len.de>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        Dongseok Yi <dseok.yi@...sung.com>,
        Yadu Kishore <kyk.segfault@...il.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Marco Elver <elver@...gle.com>,
        Alexander Duyck <alexanderduyck@...com>,
        "Michael S. Tsirkin" <mst@...hat.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH net] skbuff: back tiny skbs with kmalloc() in __netdev_alloc_skb() too

Commit 3226b158e67c ("net: avoid 32 x truesize under-estimation for
tiny skbs") ensured that skbs with data size lower than 1025 bytes
will be kmalloc'ed to avoid excessive page cache fragmentation and
memory consumption.
However, the same issue can still be achieved manually via
__netdev_alloc_skb(), where the check for size hasn't been changed.
Mirror the condition from __napi_alloc_skb() to prevent from that.

Fixes: 3226b158e67c ("net: avoid 32 x truesize under-estimation for tiny skbs")
Signed-off-by: Alexander Lobakin <alobakin@...me>
---
 net/core/skbuff.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index c1a6f262636a..785daff48030 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -437,7 +437,11 @@ struct sk_buff *__netdev_alloc_skb(struct net_device *dev, unsigned int len,
 
 	len += NET_SKB_PAD;
 
-	if ((len > SKB_WITH_OVERHEAD(PAGE_SIZE)) ||
+	/* If requested length is either too small or too big,
+	 * we use kmalloc() for skb->head allocation.
+	 */
+	if (len <= SKB_WITH_OVERHEAD(1024) ||
+	    len > SKB_WITH_OVERHEAD(PAGE_SIZE) ||
 	    (gfp_mask & (__GFP_DIRECT_RECLAIM | GFP_DMA))) {
 		skb = __alloc_skb(len, gfp_mask, SKB_ALLOC_RX, NUMA_NO_NODE);
 		if (!skb)
-- 
2.30.0