netdev - Re: [PATCH v2 net-next] net: shrink napi_skb_cache_{put,get}() and napi_skb_cache_get

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAAVpQUDz0B_49t82RpsH-Fdvukr9oVxur3TvDm8FNQyXgVTU5g@mail.gmail.com>
Date: Thu, 16 Oct 2025 22:33:01 -0700
From: Kuniyuki Iwashima <kuniyu@...gle.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, Alexander Lobakin <aleksander.lobakin@...el.com>
Subject: Re: [PATCH v2 net-next] net: shrink napi_skb_cache_{put,get}() and napi_skb_cache_get_bulk()

On Thu, Oct 16, 2025 at 11:29 AM Eric Dumazet <edumazet@...gle.com> wrote:
>
> 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 not an inline and not const,
> and kasan_unpoison_object_data() is an inline function.
>
> Cache kmem_cache_size() result in a variable, so that
> the compiler can remove dead code (and variable) when/if
> CONFIG_KASAN is unset.
>
> After this patch, napi_skb_cache_put() is inlined in its callers,
> and we avoid one kmem_cache_size() call in napi_skb_cache_get()
> and napi_skb_cache_get_bulk().
>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Reviewed-by: Kuniyuki Iwashima <kuniyu@...gle.com>