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Message-ID: <59a875a9-2072-467d-8989-f01525ecd08c@intel.com>
Date: Fri, 25 Oct 2024 17:12:27 +0200
From: Alexander Lobakin <aleksander.lobakin@...el.com>
To: Justin Iurman <justin.iurman@...ege.be>
CC: <netdev@...r.kernel.org>, <davem@...emloft.net>, <dsahern@...nel.org>,
<edumazet@...gle.com>, <kuba@...nel.org>, <pabeni@...hat.com>,
<horms@...nel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next 1/3] net: ipv6: ioam6_iptunnel: mitigate
2-realloc issue
From: Justin Iurman <justin.iurman@...ege.be>
Date: Fri, 25 Oct 2024 15:37:25 +0200
> This patch mitigates the two-reallocations issue with ioam6_iptunnel by
> providing the dst_entry (in the cache) to the first call to
> skb_cow_head(). As a result, the very first iteration would still
> trigger two reallocations (i.e., empty cache), while next iterations
> would only trigger a single reallocation.
[...]
> static int ioam6_do_inline(struct net *net, struct sk_buff *skb,
> - struct ioam6_lwt_encap *tuninfo)
> + struct ioam6_lwt_encap *tuninfo,
> + struct dst_entry *dst)
> {
> struct ipv6hdr *oldhdr, *hdr;
> int hdrlen, err;
>
> hdrlen = (tuninfo->eh.hdrlen + 1) << 3;
>
> - err = skb_cow_head(skb, hdrlen + skb->mac_len);
> + err = skb_cow_head(skb, hdrlen + (!dst ? skb->mac_len
> + : LL_RESERVED_SPACE(dst->dev)));
You use this pattern a lot throughout the series. I believe you should
make a static inline or a macro from it.
static inline u32 some_name(const *dst, const *skb)
{
return dst ? LL_RESERVED_SPACE(dst->dev) : skb->mac_len;
}
BTW why do you check for `!dst`, not `dst`? Does changing this affects
performance?
> if (unlikely(err))
> return err;
Thanks,
Olek
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