linux-kernel - Re: [PATCH net-next V2 06/11] net/mlx5e: SHAMPO: Separate pool for headers

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Message-ID: <20250527082956.12e57fe5@kernel.org>
Date: Tue, 27 May 2025 08:29:56 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Saeed Mahameed <saeed@...nel.org>
Cc: Tariq Toukan <tariqt@...dia.com>, "David S. Miller"
 <davem@...emloft.net>, Paolo Abeni <pabeni@...hat.com>, Eric Dumazet
 <edumazet@...gle.com>, Andrew Lunn <andrew+netdev@...n.ch>, Saeed Mahameed
 <saeedm@...dia.com>, Leon Romanovsky <leon@...nel.org>, Richard Cochran
 <richardcochran@...il.com>, Alexei Starovoitov <ast@...nel.org>, Daniel
 Borkmann <daniel@...earbox.net>, Jesper Dangaard Brouer <hawk@...nel.org>,
 John Fastabend <john.fastabend@...il.com>, netdev@...r.kernel.org,
 linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
 bpf@...r.kernel.org, Moshe Shemesh <moshe@...dia.com>, Mark Bloch
 <mbloch@...dia.com>, Gal Pressman <gal@...dia.com>, Cosmin Ratiu
 <cratiu@...dia.com>, Dragos Tatulea <dtatulea@...dia.com>
Subject: Re: [PATCH net-next V2 06/11] net/mlx5e: SHAMPO: Separate pool for
 headers

On Thu, 22 May 2025 16:08:48 -0700 Saeed Mahameed wrote:
> On 22 May 15:30, Jakub Kicinski wrote:
> >On Fri, 23 May 2025 00:41:21 +0300 Tariq Toukan wrote:  
> >> Allocate a separate page pool for headers when SHAMPO is enabled.
> >> This will be useful for adding support to zc page pool, which has to be
> >> different from the headers page pool.  
> >
> >Could you explain why always allocate a separate pool?  
> 
> Better flow management, 0 conditional code on data path to alloc/return
> header buffers, since in mlx5 we already have separate paths to handle
> header, we don't have/need bnxt_separate_head_pool() and
> rxr->need_head_pool spread across the code.. 
> 
> Since we alloc and return pages in bulks, it makes more sense to manage
> headers and data in separate pools if we are going to do it anyway for 
> "undreadable_pools", and when there's no performance impact.

I think you need to look closer at the bnxt implementation.
There is no conditional on the buffer alloc path. If the head and
payload pools are identical we simply assign the same pointer to 
(using mlx5 naming) page_pool and hd_page_pool.

Your arguments are not very convincing, TBH.
The memory sitting in the recycling rings is very much not free.