netdev - RE: [PATCH V4,net-next] net: mana: Add page pool for RX buffers

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Date: Tue, 1 Aug 2023 14:19:56 +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
	<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>, "john.fastabend@...il.com"
	<john.fastabend@...il.com>, "bpf@...r.kernel.org" <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 V4,net-next] net: mana: Add page pool for RX buffers



> -----Original Message-----
> From: Jakub Kicinski <kuba@...nel.org>
> Sent: Monday, July 31, 2023 8:31 PM
> 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 V4,net-next] net: mana: Add page pool for RX buffers
>
> On Fri, 28 Jul 2023 14:46:07 -0700 Haiyang Zhang wrote:
> >  static void *mana_get_rxfrag(struct mana_rxq *rxq, struct device *dev,
> > -                        dma_addr_t *da, bool is_napi)
> > +                        dma_addr_t *da, bool *from_pool, bool is_napi)
> >  {
> >     struct page *page;
> >     void *va;
> >
> > +   *from_pool = false;
> > +
> >     /* Reuse XDP dropped page if available */
> >     if (rxq->xdp_save_va) {
> >             va = rxq->xdp_save_va;
> > @@ -1533,17 +1543,22 @@ static void *mana_get_rxfrag(struct mana_rxq
> *rxq, struct device *dev,
> >                     return NULL;
> >             }
> >     } else {
> > -           page = dev_alloc_page();
> > +           page = page_pool_dev_alloc_pages(rxq->page_pool);
> >             if (!page)
> >                     return NULL;
> >
> > +           *from_pool = true;
> >             va = page_to_virt(page);
> >     }
> >
> >     *da = dma_map_single(dev, va + rxq->headroom, rxq->datasize,
> >                          DMA_FROM_DEVICE);
> >     if (dma_mapping_error(dev, *da)) {
> > -           put_page(virt_to_head_page(va));
> > +           if (*from_pool)
> > +                   page_pool_put_full_page(rxq->page_pool, page,
> is_napi);
>
> AFAICT you only pass the is_napi to recycle in case of error?
> It's fine to always pass in false, passing true enables some
> optimizations but it's not worth trying to optimize error paths.

Yes, this place is only for the error path. I will pass in false.

>
> Otherwise you may be passing in true, even tho budget was 0,
> see the recently added warnings in this doc:
>
> https://www.ker/
> nel.org%2Fdoc%2Fhtml%2Fnext%2Fnetworking%2Fnapi.html&data=05%7C01%7
> Chaiyangz%40microsoft.com%7C82fcd2d20fe54dd8cd4808db9226a2c7%7C72f9
> 88bf86f141af91ab2d7cd011db47%7C1%7C0%7C638264466881746523%7CUnkn
> own%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1ha
> WwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=D9ac4TnYOSPwGmk%2FKX
> G4buu%2FKT7J%2BuH8lAJNPl%2FRWy4%3D&reserved=0
>
> In general the driver seems to be processing Rx regardless
> of budget? This looks like a bug which should be fixed with
> a separate patch for the net tree..

Thanks, I will look into and fix this in a separate patch.

- Haiyang