Re: [PATCH net-next v2] netdevice: define and allocate &net_device _properly_

Simon Horman
2024-07-09T18:11:34Z

On Tue, Jul 09, 2024 at 05:54:25AM -0700, Breno Leitao wrote:
> From: Alexander Lobakin <aleksander.lobakin@intel.com>
>
> In fact, this structure contains a flexible array at the end, but
> historically its size, alignment etc., is calculated manually.
> There are several instances of the structure embedded into other
> structures, but also there's ongoing effort to remove them and we
> could in the meantime declare &net_device properly.
> Declare the array explicitly, use struct_size() and store the array
> size inside the structure, so that __counted_by() can be applied.
> Don't use PTR_ALIGN(), as SLUB itself tries its best to ensure the
> allocated buffer is aligned to what the user expects.
> Also, change its alignment from %NETDEV_ALIGN to the cacheline size
> as per several suggestions on the netdev ML.
>
> bloat-o-meter for vmlinux:
>
> free_netdev 445 440 -5
> netdev_freemem 24 - -24
> alloc_netdev_mqs 1481 1450 -31
>
> On x86_64 with several NICs of different vendors, I was never able to
> get a &net_device pointer not aligned to the cacheline size after the
> change.
>
> Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
> Signed-off-by: Breno Leitao <leitao@debian.org>
> Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>

Hi Breno,

Some kernel doc warnings from my side.

Flagged by: kernel-doc -none

> ---
> Changelog:
>
> v2:
> * Rebased Alexander's patch on top of f750dfe825b90 ("ethtool: provide
> customized dim profile management").
> * Removed the ALIGN() of SMP_CACHE_BYTES for sizeof_priv.
>
> v1:
> * https://lore.kernel.org/netdev/90fd7cd7-72dc-4df6-88ec-fbc8b64735ad@intel.com
>
> include/linux/netdevice.h | 12 +++++++-----
> net/core/dev.c | 30 ++++++------------------------
> net/core/net-sysfs.c | 2 +-
> 3 files changed, 14 insertions(+), 30 deletions(-)
>
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 93558645c6d0..f0dd499244d4 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -2199,10 +2199,10 @@ struct net_device {
> unsigned short neigh_priv_len;
> unsigned short dev_id;
> unsigned short dev_port;
> - unsigned short padded;

padded should also be removed from the Kernel doc for this structure.

> + int irq;
> + u32 priv_len;

And irq and priv_len should be added to the Kernel doc for this structure.

>
> spinlock_t addr_list_lock;
> - int irq;
>
> struct netdev_hw_addr_list uc;
> struct netdev_hw_addr_list mc;

...