netdev - Re: [PATCH net-next v2 2/3] page_pool: Turn dma_sync and dma_sync

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Message-ID: <20250325151743.7ae425c3@kernel.org>
Date: Tue, 25 Mar 2025 15:17:43 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Toke Høiland-Jørgensen <toke@...hat.com>
Cc: "David S. Miller" <davem@...emloft.net>, Jesper Dangaard Brouer
 <hawk@...nel.org>, Saeed Mahameed <saeedm@...dia.com>, Leon Romanovsky
 <leon@...nel.org>, Tariq Toukan <tariqt@...dia.com>, Andrew Lunn
 <andrew+netdev@...n.ch>, Eric Dumazet <edumazet@...gle.com>, Paolo Abeni
 <pabeni@...hat.com>, Ilias Apalodimas <ilias.apalodimas@...aro.org>, Simon
 Horman <horms@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, Mina
 Almasry <almasrymina@...gle.com>, Yonglong Liu <liuyonglong@...wei.com>,
 Yunsheng Lin <linyunsheng@...wei.com>, Pavel Begunkov
 <asml.silence@...il.com>, Matthew Wilcox <willy@...radead.org>,
 netdev@...r.kernel.org, bpf@...r.kernel.org, linux-rdma@...r.kernel.org,
 linux-mm@...ck.org
Subject: Re: [PATCH net-next v2 2/3] page_pool: Turn dma_sync and
 dma_sync_cpu fields into a bitmap

On Tue, 25 Mar 2025 16:45:43 +0100 Toke Høiland-Jørgensen wrote:
> Change the single-bit booleans for dma_sync into an unsigned long with
> BIT() definitions so that a subsequent patch can write them both with a
> singe WRITE_ONCE() on teardown. Also move the check for the sync_cpu
> side into __page_pool_dma_sync_for_cpu() so it can be disabled for
> non-netmem providers as well.

Can we make them just bools without the bit width?
Less churn and actually fewer bytes.
I don't see why we'd need to wipe them atomically.
In fact I don't see why we're touching dma_sync_cpu, at all,
it's driver-facing and the driver is gone in the problematic
scenario.