netdev - Re: [PATCH net-next v3 2/3] page_pool: Turn dma

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Message-ID: <b025e2b7-ff99-4659-811c-8071d4aa8031@intel.com>
Date: Wed, 26 Mar 2025 18:40:27 +0100
From: Alexander Lobakin <aleksander.lobakin@...el.com>
To: Toke Høiland-Jørgensen <toke@...hat.com>
CC: "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>,
	<netdev@...r.kernel.org>, <bpf@...r.kernel.org>,
	<linux-rdma@...r.kernel.org>, <linux-mm@...ck.org>
Subject: Re: [PATCH net-next v3 2/3] page_pool: Turn dma_sync into a
 full-width bool field

From: Toke Høiland-Jørgensen <toke@...hat.com>
Date: Wed, 26 Mar 2025 09:18:39 +0100

> Change the single-bit boolean for dma_sync into a full-width bool, so we
> can read it as volatile with READ_ONCE(). A subsequent patch will add
> writing with WRITE_ONCE() on teardown.

Don't we have something like READ_ONCE(), but for one bit? Like
atomic-load-blah?

> 
> Reviewed-by: Mina Almasry <almasrymina@...gle.com>
> Tested-by: Yonglong Liu <liuyonglong@...wei.com>
> Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
> ---
>  include/net/page_pool/types.h | 6 +++---
>  net/core/page_pool.c          | 2 +-
>  2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/include/net/page_pool/types.h b/include/net/page_pool/types.h
> index df0d3c1608929605224feb26173135ff37951ef8..d6c93150384fbc4579bb0d0afb357ebb26c564a3 100644
> --- a/include/net/page_pool/types.h
> +++ b/include/net/page_pool/types.h
> @@ -173,10 +173,10 @@ struct page_pool {
>  	int cpuid;
>  	u32 pages_state_hold_cnt;
>  
> -	bool has_init_callback:1;	/* slow::init_callback is set */
> +	bool dma_sync;				/* Perform DMA sync for device */
> +	bool dma_sync_for_cpu:1;		/* Perform DMA sync for cpu */
>  	bool dma_map:1;			/* Perform DMA mapping */
> -	bool dma_sync:1;		/* Perform DMA sync for device */
> -	bool dma_sync_for_cpu:1;	/* Perform DMA sync for cpu */
> +	bool has_init_callback:1;	/* slow::init_callback is set */
>  #ifdef CONFIG_PAGE_POOL_STATS
>  	bool system:1;			/* This is a global percpu pool */
>  #endif
> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> index acef1fcd8ddcfd1853a6f2055c1f1820ab248e8d..fb32768a97765aacc7f1103bfee38000c988b0de 100644
> --- a/net/core/page_pool.c
> +++ b/net/core/page_pool.c
> @@ -466,7 +466,7 @@ page_pool_dma_sync_for_device(const struct page_pool *pool,
>  			      netmem_ref netmem,
>  			      u32 dma_sync_size)
>  {
> -	if (pool->dma_sync && dma_dev_need_sync(pool->p.dev))
> +	if (READ_ONCE(pool->dma_sync) && dma_dev_need_sync(pool->p.dev))
>  		__page_pool_dma_sync_for_device(pool, netmem, dma_sync_size);
>  }

Thanks,
Olek