From: Jakub Kicinski <kuba@kernel.org>
To: Eric Dumazet <edumazet@google.com>
Cc: Paolo Abeni <pabeni@redhat.com>,
"David S . Miller" <davem@davemloft.net>,
netdev@vger.kernel.org, eric.dumazet@gmail.com,
Alexander Duyck <alexanderduyck@fb.com>,
Soheil Hassas Yeganeh <soheil@google.com>
Subject: Re: [PATCH net-next 4/4] net: add dedicated kmem_cache for typical/small skb->head
Date: Fri, 3 Feb 2023 11:47:44 -0800 [thread overview]
Message-ID: <20230203114744.153c4063@kernel.org> (raw)
In-Reply-To: <CANn89iLj8hC7jgb5jDNi01nKqikGbgKMtFvbZDxWi4Qoi1y8fw@mail.gmail.com>
On Fri, 3 Feb 2023 09:17:55 +0100 Eric Dumazet wrote:
> > I *think* non power of two size is also required to avoid an issue
> > plain (no GFP_DMA nor __GFP_ACCOUNT) allocations in case of fallback to
> > kmalloc(), to prevent skb_kfree_head() mis-interpreting skb->head as
> > kmem_cache allocated.
>
> Indeed there are multiple cases explaining why SKB_SMALL_HEAD_CACHE_SIZE
> needs to be a non power of two.
Since you may need to respin would you mind spelling this out a bit
more in the comment ? Maybe:
-/* We want SKB_SMALL_HEAD_CACHE_SIZE to not be a power of two. */
+/* We want SKB_SMALL_HEAD_CACHE_SIZE to not be a power of two.
+ * This should ensure that SKB_SMALL_HEAD_HEADROOM is a unique
+ * size, and we can differentiate heads from skb_small_head_cache
+ * vs system slabs by looking at their size (skb_end_offset()).
+ */
next prev parent reply other threads:[~2023-02-03 19:47 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-02 18:57 [PATCH net-next 0/4] net: core: use a dedicated kmem_cache for skb head allocs Eric Dumazet
2023-02-02 18:57 ` [PATCH net-next 1/4] net: add SKB_HEAD_ALIGN() helper Eric Dumazet
2023-02-02 20:06 ` Soheil Hassas Yeganeh
2023-02-02 18:57 ` [PATCH net-next 2/4] net: remove osize variable in __alloc_skb() Eric Dumazet
2023-02-02 20:07 ` Soheil Hassas Yeganeh
2023-02-02 18:58 ` [PATCH net-next 3/4] net: factorize code in kmalloc_reserve() Eric Dumazet
2023-02-02 20:09 ` Soheil Hassas Yeganeh
2023-02-02 18:58 ` [PATCH net-next 4/4] net: add dedicated kmem_cache for typical/small skb->head Eric Dumazet
2023-02-02 20:14 ` Soheil Hassas Yeganeh
2023-02-03 5:11 ` Jakub Kicinski
2023-02-03 7:00 ` Eric Dumazet
2023-02-03 7:59 ` Paolo Abeni
2023-02-03 8:17 ` Eric Dumazet
2023-02-03 19:47 ` Jakub Kicinski [this message]
2023-02-03 19:37 ` kernel test robot
2023-02-03 19:42 ` Jakub Kicinski
2023-02-06 18:16 ` [PATCH net-next 0/4] net: core: use a dedicated kmem_cache for skb head allocs Paolo Abeni
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