netdev - Re: [PATCH net-next 4/4] net: inline get_netmem() and put

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Message-ID: <aXfN+/v8JAh9GcQU@devvm11784.nha0.facebook.com>
Date: Mon, 26 Jan 2026 12:26:35 -0800
From: Bobby Eshleman <bobbyeshleman@...il.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: "David S . Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>, netdev@...r.kernel.org,
	eric.dumazet@...il.com
Subject: Re: [PATCH net-next 4/4] net: inline get_netmem() and put_netmem()

On Thu, Jan 22, 2026 at 04:57:19AM +0000, Eric Dumazet wrote:
> These helpers are used in network fast paths.
> 
> Only call out-of-line helpers for netmem case.
> 
> We might consider inlining __get_netmem() and __put_netmem()
> in the future.
> 
> $ scripts/bloat-o-meter -t vmlinux.3 vmlinux.4
> add/remove: 6/6 grow/shrink: 22/1 up/down: 2614/-646 (1968)
> Function                                     old     new   delta
> pskb_carve                                  1669    1894    +225
> gro_pull_from_frag0                            -     206    +206
> get_page                                     190     380    +190
> skb_segment                                 3561    3747    +186
> put_page                                     595     765    +170
> skb_copy_ubufs                              1683    1822    +139
> __pskb_trim_head                             276     401    +125
> __pskb_copy_fclone                           734     858    +124
> skb_zerocopy                                1092    1215    +123
> pskb_expand_head                             892    1008    +116
> skb_split                                    828     940    +112
> skb_release_data                             297     409    +112
> ___pskb_trim                                 829     941    +112
> __skb_zcopy_downgrade_managed                120     226    +106
> tcp_clone_payload                            530     634    +104
> esp_ssg_unref                                191     294    +103
> dev_gro_receive                             1464    1514     +50
> __put_netmem                                   -      41     +41
> __get_netmem                                   -      41     +41
> skb_shift                                   1139    1175     +36
> skb_try_coalesce                             681     714     +33
> __pfx_put_page                               112     144     +32
> __pfx_get_page                                32      64     +32
> __pskb_pull_tail                            1137    1168     +31
> veth_xdp_get                                 250     267     +17
> __pfx_gro_pull_from_frag0                      -      16     +16
> __pfx___put_netmem                             -      16     +16
> __pfx___get_netmem                             -      16     +16
> __pfx_put_netmem                              16       -     -16
> __pfx_gro_try_pull_from_frag0                 16       -     -16
> __pfx_get_netmem                              16       -     -16
> put_netmem                                   114       -    -114
> get_netmem                                   130       -    -130
> napi_gro_frags                               929     771    -158
> gro_try_pull_from_frag0                      196       -    -196
> Total: Before=22565857, After=22567825, chg +0.01%
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> ---
>  include/net/netmem.h | 20 ++++++++++++++++++--
>  net/core/skbuff.c    | 31 ++++++++++---------------------
>  2 files changed, 28 insertions(+), 23 deletions(-)
> 
> diff --git a/include/net/netmem.h b/include/net/netmem.h
> index 2113a197abb315f608ee3d6d3e8a60811b3781f8..a96b3e5e5574c1800ae7949c39366968707ab5d5 100644
> --- a/include/net/netmem.h
> +++ b/include/net/netmem.h
> @@ -401,8 +401,24 @@ static inline bool net_is_devmem_iov(const struct net_iov *niov)
>  }
>  #endif
>  
> -void get_netmem(netmem_ref netmem);
> -void put_netmem(netmem_ref netmem);
> +void __get_netmem(netmem_ref netmem);
> +void __put_netmem(netmem_ref netmem);
> +
> +static __always_inline void get_netmem(netmem_ref netmem)
> +{
> +	if (netmem_is_net_iov(netmem))
> +		__get_netmem(netmem);
> +	else
> +		get_page(netmem_to_page(netmem));
> +}
> +
> +static __always_inline void put_netmem(netmem_ref netmem)
> +{
> +	if (netmem_is_net_iov(netmem))
> +		__put_netmem(netmem);
> +	else
> +		put_page(netmem_to_page(netmem));
> +}
>  
>  #define netmem_dma_unmap_addr_set(NETMEM, PTR, ADDR_NAME, VAL)   \
>  	do {                                                     \
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index c57c806edba8524d3d498800e61ae6901fbfe5fb..2a8235c3d6f7fcee8b0b28607c10db985965b8d4 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -7422,31 +7422,20 @@ bool csum_and_copy_from_iter_full(void *addr, size_t bytes,
>  }
>  EXPORT_SYMBOL(csum_and_copy_from_iter_full);
>  
> -void get_netmem(netmem_ref netmem)
> +void __get_netmem(netmem_ref netmem)
>  {
> -	struct net_iov *niov;
> +	struct net_iov *niov = netmem_to_net_iov(netmem);
>  
> -	if (netmem_is_net_iov(netmem)) {
> -		niov = netmem_to_net_iov(netmem);
> -		if (net_is_devmem_iov(niov))
> -			net_devmem_get_net_iov(netmem_to_net_iov(netmem));
> -		return;
> -	}
> -	get_page(netmem_to_page(netmem));
> +	if (net_is_devmem_iov(niov))
> +		net_devmem_get_net_iov(netmem_to_net_iov(netmem));

I wonder if this is a good time to move to just re-use niov from above
here instead of re-convert with netmem_to_net_iov()? I do acknowledge
the original code did not do this.

Best,
Bobby