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

From: Przemek Kitszel
Date: Tue May 07 2024 - 11:31:43 EST


On 5/7/24 14:39, Alexander Lobakin wrote:
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@xxxxxxxxx>
---
include/linux/netdevice.h | 12 +++++++-----
net/core/dev.c | 31 +++++++------------------------
net/core/net-sysfs.c | 2 +-
3 files changed, 15 insertions(+), 30 deletions(-)


Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@xxxxxxxxx>