netdev - Re: [PATCH net-next] bnxt: fill data page pool with frags if PAGE_SIZE > BNXT_RX_PAGE

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Message-ID: <CACKFLimKpAtt8GDGT7k5zagQfzmPc_ggt9c0pu427=+T_FST1g@mail.gmail.com>
Date: Mon, 11 Aug 2025 11:08:04 -0700
From: Michael Chan <michael.chan@...adcom.com>
To: David Wei <dw@...idwei.uk>
Cc: netdev@...r.kernel.org, Pavan Chebbi <pavan.chebbi@...adcom.com>, 
	Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net-next] bnxt: fill data page pool with frags if
 PAGE_SIZE > BNXT_RX_PAGE_SIZE

On Mon, Aug 11, 2025 at 10:43 AM David Wei <dw@...idwei.uk> wrote:
>
> The data page pool always fills the HW rx ring with pages. On arm64 with
> 64K pages, this will waste _at least_ 32K of memory per entry in the rx
> ring.
>
> Fix by fragmenting the pages if PAGE_SIZE > BNXT_RX_PAGE_SIZE. This
> makes the data page pool the same as the header pool.
>
> Tested with iperf3 with a small (64 entries) rx ring to encourage buffer
> circulation.

This was a regression when adding devmem support.  Prior to that,
__bnxt_alloc_rx_page() would handle this properly.  Should we add a
Fixes tag?

The patch looks good to me.  Thanks.
Reviewed-by: Michael Chan <michael.chan@...adocm.com>

>
> Signed-off-by: David Wei <dw@...idwei.uk>
> ---
>  drivers/net/ethernet/broadcom/bnxt/bnxt.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt.c b/drivers/net/ethernet/broadcom/bnxt/bnxt.c
> index 5578ddcb465d..9d7631ce860f 100644
> --- a/drivers/net/ethernet/broadcom/bnxt/bnxt.c
> +++ b/drivers/net/ethernet/broadcom/bnxt/bnxt.c
> @@ -926,15 +926,21 @@ static struct page *__bnxt_alloc_rx_page(struct bnxt *bp, dma_addr_t *mapping,
>
>  static netmem_ref __bnxt_alloc_rx_netmem(struct bnxt *bp, dma_addr_t *mapping,
>                                          struct bnxt_rx_ring_info *rxr,
> +                                        unsigned int *offset,
>                                          gfp_t gfp)
>  {
>         netmem_ref netmem;
>
> -       netmem = page_pool_alloc_netmems(rxr->page_pool, gfp);
> +       if (PAGE_SIZE > BNXT_RX_PAGE_SIZE) {
> +               netmem = page_pool_alloc_frag_netmem(rxr->page_pool, offset, BNXT_RX_PAGE_SIZE, gfp);
> +       } else {
> +               netmem = page_pool_alloc_netmems(rxr->page_pool, gfp);
> +               *offset = 0;
> +       }
>         if (!netmem)
>                 return 0;
>
> -       *mapping = page_pool_get_dma_addr_netmem(netmem);
> +       *mapping = page_pool_get_dma_addr_netmem(netmem) + *offset;
>         return netmem;
>  }
>
> @@ -1029,7 +1035,7 @@ static int bnxt_alloc_rx_netmem(struct bnxt *bp, struct bnxt_rx_ring_info *rxr,
>         dma_addr_t mapping;
>         netmem_ref netmem;
>
> -       netmem = __bnxt_alloc_rx_netmem(bp, &mapping, rxr, gfp);
> +       netmem = __bnxt_alloc_rx_netmem(bp, &mapping, rxr, &offset, gfp);
>         if (!netmem)
>                 return -ENOMEM;
>
> --
> 2.47.3
>

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