netdev - Re: [PATCH v2] net: mana: Use page pool fragments for RX buffers instead of full pages to improve memory efficiency.

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Message-ID: <73add9b2-2155-4c4f-92bb-8166138b226b@kernel.org>
Date: Tue, 29 Jul 2025 12:15:23 +0200
From: Jesper Dangaard Brouer <hawk@...nel.org>
To: Dipayaan Roy <dipayanroy@...ux.microsoft.com>, horms@...nel.org,
 kuba@...nel.org, kys@...rosoft.com, haiyangz@...rosoft.com,
 wei.liu@...nel.org, decui@...rosoft.com, andrew+netdev@...n.ch,
 davem@...emloft.net, edumazet@...gle.com, pabeni@...hat.com,
 longli@...rosoft.com, kotaranov@...rosoft.com, ast@...nel.org,
 daniel@...earbox.net, john.fastabend@...il.com, sdf@...ichev.me,
 lorenzo@...nel.org, michal.kubiak@...el.com, ernis@...ux.microsoft.com,
 shradhagupta@...ux.microsoft.com, shirazsaleem@...rosoft.com,
 rosenp@...il.com, netdev@...r.kernel.org, linux-hyperv@...r.kernel.org,
 linux-rdma@...r.kernel.org, bpf@...r.kernel.org,
 linux-kernel@...r.kernel.org, ssengar@...ux.microsoft.com,
 dipayanroy@...rosoft.com
Cc: Chris Arges <carges@...udflare.com>,
 kernel-team <kernel-team@...udflare.com>, Tariq Toukan <tariqt@...dia.com>,
 Saeed Mahameed <saeedm@...dia.com>, Dragos Tatulea <dtatulea@...dia.com>,
 Yunsheng Lin <linyunsheng@...wei.com>
Subject: Re: [PATCH v2] net: mana: Use page pool fragments for RX buffers
 instead of full pages to improve memory efficiency.

On 23/07/2025 21.07, Dipayaan Roy wrote:
> This patch enhances RX buffer handling in the mana driver by allocating
> pages from a page pool and slicing them into MTU-sized fragments, rather
> than dedicating a full page per packet. This approach is especially
> beneficial on systems with large page sizes like 64KB.
> 
> Key improvements:
> 
> - Proper integration of page pool for RX buffer allocations.
> - MTU-sized buffer slicing to improve memory utilization.
> - Reduce overall per Rx queue memory footprint.
> - Automatic fallback to full-page buffers when:
>     * Jumbo frames are enabled (MTU > PAGE_SIZE / 2).
>     * The XDP path is active, to avoid complexities with fragment reuse.
> - Removal of redundant pre-allocated RX buffers used in scenarios like MTU
>    changes, ensuring consistency in RX buffer allocation.
> 
> Testing on VMs with 64KB pages shows around 200% throughput improvement.
> Memory efficiency is significantly improved due to reduced wastage in page
> allocations. Example: We are now able to fit 35 rx buffers in a single 64kb
> page for MTU size of 1500, instead of 1 rx buffer per page previously.
> 
> Tested:
> 
> - iperf3, iperf2, and nttcp benchmarks.
> - Jumbo frames with MTU 9000.
> - Native XDP programs (XDP_PASS, XDP_DROP, XDP_TX, XDP_REDIRECT) for
>    testing the XDP path in driver.
> - Page leak detection (kmemleak).
> - Driver load/unload, reboot, and stress scenarios.

Chris (Cc) discovered a crash/bug[1] with page pool fragments used from 
the mlx5 driver.
He put together a BPF program that reproduces the issue here:
- [2] https://github.com/arges/xdp-redirector

Can I ask you to test that your driver against this reproducer?

[1] https://lore.kernel.org/all/aIEuZy6fUj_4wtQ6@861G6M3/

--Jesper