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

[Haiyang Zhang]

> -----Original Message-----
> From: Jakub Kicinski <kuba@xxxxxxxxxx>
> Sent: Monday, July 31, 2023 8:31 PM
> To: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
> Cc: linux-hyperv@xxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; Dexuan Cui
> <decui@xxxxxxxxxxxxx>; KY Srinivasan <kys@xxxxxxxxxxxxx>; Paul Rosswurm
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> ast@xxxxxxxxxx; Ajay Sharma <sharmaajay@xxxxxxxxxxxxx>; hawk@xxxxxxxxxx;
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> kernel@xxxxxxxxxxxxxxx
> 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