netdev - RE: [PATCH V2,net-next] net: mana: Add page pool for RX buffers

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Date: Thu, 20 Jul 2023 13:15:36 +0000
From: Haiyang Zhang <haiyangz@...rosoft.com>
To: Jakub Kicinski <kuba@...nel.org>
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>, "daniel@...earbox.net" <daniel@...earbox.net>,
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	<bpf@...r.kernel.org>, "ast@...nel.org" <ast@...nel.org>, Ajay Sharma
	<sharmaajay@...rosoft.com>, "hawk@...nel.org" <hawk@...nel.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>, "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



> -----Original Message-----
> From: Jakub Kicinski <kuba@...nel.org>
> Sent: Thursday, July 20, 2023 12:30 AM
> To: Haiyang Zhang <haiyangz@...rosoft.com>
> Cc: linux-hyperv@...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; vkuznets@...hat.com;
> davem@...emloft.net; wei.liu@...nel.org; edumazet@...gle.com;
> pabeni@...hat.com; leon@...nel.org; Long Li <longli@...rosoft.com>;
> ssengar@...ux.microsoft.com; linux-rdma@...r.kernel.org;
> daniel@...earbox.net; john.fastabend@...il.com; bpf@...r.kernel.org;
> ast@...nel.org; Ajay Sharma <sharmaajay@...rosoft.com>; hawk@...nel.org;
> tglx@...utronix.de; shradhagupta@...ux.microsoft.com; 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

Thank you for the comments.
I will update the patch.

- Haiyang