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

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Message-ID: <87msdjhfl5.fsf@toke.dk>
Date: Mon, 17 Mar 2025 15:55:18 +0100
From: Toke Høiland-Jørgensen <toke@...hat.com>
To: Yunsheng Lin <yunshenglin0825@...il.com>, "David S. Miller"
 <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 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>
Cc: netdev@...r.kernel.org, bpf@...r.kernel.org, linux-rdma@...r.kernel.org,
 linux-mm@...ck.org
Subject: Re: [PATCH net-next 2/3] page_pool: Turn dma_sync and dma_sync_cpu
 fields into a bitmap

Yunsheng Lin <yunshenglin0825@...il.com> writes:

> On 3/14/2025 6:10 PM, 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.
>
> I guess this patch is for the preparation of disabling the
> page_pool_dma_sync_for_cpu() related API on teardown?
>
> It seems unnecessary that page_pool_dma_sync_for_cpu() related API need
> to be disabled on teardown as page_pool_dma_sync_for_cpu() has the same
> calling assumption as the alloc API, which is not supposed to be called
> by the drivers when page_pool_destroy() is called.

Sure, we could keep it to the dma_sync_for_dev() direction only, but
making both directions use the same variable to store the state, and
just resetting it at once, seemed simpler and more consistent.

-Toke