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

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Message-ID: <20250326042347.279f23a8@kernel.org>
Date: Wed, 26 Mar 2025 04:23:47 -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 Wed, 26 Mar 2025 09:12:34 +0100 Toke Høiland-Jørgensen wrote:
> > 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.  
> 
> No you're right, but it felt weird to change just one of them, so
> figured I'd go with both. But keeping them both as bool, and just making
> dma_sync a full-width bool works, so I'll respin with that and leave
> dma_sync_cpu as-is.

Opinion on dma_sync_cpu clearing probably depends on mental model.
No strong feelings but perhaps add a comment next to clearing it
for the likes of myself saying that this technically shouldn't be
needed as we only expect drivers to ask for CPU sync?