netdev - Re: [PATCH net-next] net: shrink napi_skb_cache

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: <CANn89iJo-b=B7jUtbazcCtgKJrnbgdEXJ-OPvOwFziP_OSLaYA@mail.gmail.com>
Date: Thu, 16 Oct 2025 06:36:55 -0700
From: Eric Dumazet <edumazet@...gle.com>
To: Alexander Lobakin <aleksander.lobakin@...el.com>
Cc: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
	Kuniyuki Iwashima <kuniyu@...gle.com>, netdev@...r.kernel.org, eric.dumazet@...il.com
Subject: Re: [PATCH net-next] net: shrink napi_skb_cache_put()

On Thu, Oct 16, 2025 at 6:29 AM Eric Dumazet <edumazet@...gle.com> wrote:
>
> On Thu, Oct 16, 2025 at 5:56 AM Eric Dumazet <edumazet@...gle.com> wrote:
> >
> > On Thu, Oct 16, 2025 at 4:08 AM Alexander Lobakin
> > <aleksander.lobakin@...el.com> wrote:
> > >
> > > From: Eric Dumazet <edumazet@...gle.com>
> > >
> > > BTW doesn't napi_skb_cache_get() (inc. get_bulk()) suffer the same way?
> >
> > Probably, like other calls to napi_skb_cache_put(()
> >
> > No loop there, so I guess there is no big deal.
> >
> > I was looking at napi_skb_cache_put() because there is a lack of NUMA awareness,
> > and was curious to experiment with some strategies there.
>
> If we cache kmem_cache_size() in net_hotdata, the compiler is able to
> eliminate dead code
> for CONFIG_KASAN=n
>
> Maybe this looks better ?

No need to put this in net_hotdata, I was distracted by a 4byte hole
there, we can keep this hole for something  hot later.

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index bc12790017b0b5c0be99f8fb9d362b3730fa4eb0..f3b9356bebc06548a055355c5d1eb04c480f813f
100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -274,6 +274,8 @@ void *__netdev_alloc_frag_align(unsigned int
fragsz, unsigned int align_mask)
 }
 EXPORT_SYMBOL(__netdev_alloc_frag_align);

+u32 skbuff_cache_size __read_mostly;
+
 static struct sk_buff *napi_skb_cache_get(void)
 {
        struct napi_alloc_cache *nc = this_cpu_ptr(&napi_alloc_cache);
@@ -293,7 +295,7 @@ static struct sk_buff *napi_skb_cache_get(void)

        skb = nc->skb_cache[--nc->skb_count];
        local_unlock_nested_bh(&napi_alloc_cache.bh_lock);
-       kasan_mempool_unpoison_object(skb,
kmem_cache_size(net_hotdata.skbuff_cache));
+       kasan_mempool_unpoison_object(skb, skbuff_cache_size);

        return skb;
 }
@@ -1428,7 +1430,7 @@ static void napi_skb_cache_put(struct sk_buff *skb)
        if (unlikely(nc->skb_count == NAPI_SKB_CACHE_SIZE)) {
                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));
+                                               skbuff_cache_size);

                kmem_cache_free_bulk(net_hotdata.skbuff_cache,
NAPI_SKB_CACHE_HALF,
                                     nc->skb_cache + NAPI_SKB_CACHE_HALF);
@@ -5116,6 +5118,8 @@ void __init skb_init(void)
                                              offsetof(struct sk_buff, cb),
                                              sizeof_field(struct sk_buff, cb),
                                              NULL);
+       skbuff_cache_size = kmem_cache_size(net_hotdata.skbuff_cache);
+
        net_hotdata.skbuff_fclone_cache =
kmem_cache_create("skbuff_fclone_cache",
                                                sizeof(struct sk_buff_fclones),
                                                0,