linux-kernel - Re: [PATCH V2,net-next] net: mana: Add page pool for RX buffers

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Message-ID: <20230719212939.6da38bc0@kernel.org>
Date:   Wed, 19 Jul 2023 21:29:39 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Haiyang Zhang <haiyangz@...rosoft.com>
Cc:     "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Dexuan Cui <decui@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Paul Rosswurm <paulros@...rosoft.com>,
        "olaf@...fle.de" <olaf@...fle.de>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "leon@...nel.org" <leon@...nel.org>,
        Long Li <longli@...rosoft.com>,
        "ssengar@...ux.microsoft.com" <ssengar@...ux.microsoft.com>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
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        "ast@...nel.org" <ast@...nel.org>,
        Ajay Sharma <sharmaajay@...rosoft.com>,
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        "shradhagupta@...ux.microsoft.com" <shradhagupta@...ux.microsoft.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2,net-next] net: mana: Add page pool for RX buffers

On Tue, 18 Jul 2023 21:48:01 +0000 Haiyang Zhang wrote:
> Add page pool for RX buffers for faster buffer cycle and reduce CPU
> usage.
> 
> The standard page pool API is used.

> @@ -1437,8 +1437,12 @@ static void mana_rx_skb(void *buf_va, struct mana_rxcomp_oob *cqe,
>  
>  	act = mana_run_xdp(ndev, rxq, &xdp, buf_va, pkt_len);
>  
> -	if (act == XDP_REDIRECT && !rxq->xdp_rc)
> +	if (act == XDP_REDIRECT && !rxq->xdp_rc) {
> +		if (from_pool)
> +			page_pool_release_page(rxq->page_pool,
> +					       virt_to_head_page(buf_va));


IIUC you should pass the page_pool as the last argument to 
xdp_rxq_info_reg_mem_model() and then the page will be recycled
by the core, you shouldn't release it.

Not to mention the potential race in releasing the page _after_
giving its ownership to someone else.

> -		page = dev_alloc_page();
> +		if (is_napi) {
> +			page = page_pool_dev_alloc_pages(rxq->page_pool);
> +			*from_pool = true;
> +		} else {
> +			page = dev_alloc_page();

FWIW if you're only calling this outside NAPI during init, when NAPI
can't yet run, I _think_ it's okay to use page_pool_dev_alloc..

> +	pprm.pool_size = RX_BUFFERS_PER_QUEUE;
> +	pprm.napi = &cq->napi;
> +	pprm.dev = gc->dev;
> +	pprm.dma_dir = DMA_FROM_DEVICE;

If you're not setting PP_FLAG_DMA_MAP you don't have to fill in .dev
and .dma_dir
-- 
pw-bot: cr