linux-kernel - Re: [PATCH net-next v9 5/6] page_pool: update document about frag API

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Date:   Thu, 21 Sep 2023 19:59:23 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     Dima Tisnek <dimaqq@...il.com>
CC:     <davem@...emloft.net>, <kuba@...nel.org>, <pabeni@...hat.com>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Alexander Duyck <alexander.duyck@...il.com>,
        Liang Chen <liangchen.linux@...il.com>,
        Alexander Lobakin <aleksander.lobakin@...el.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        John Fastabend <john.fastabend@...il.com>,
        <linux-doc@...r.kernel.org>, <bpf@...r.kernel.org>
Subject: Re: [PATCH net-next v9 5/6] page_pool: update document about frag API

On 2023/9/21 9:02, Dima Tisnek wrote:
> Minor comment on natural language:
> 
> On Wed, Sep 20, 2023 at 9:04 PM Yunsheng Lin <linyunsheng@...wei.com> wrote:
>>
>> As more drivers begin to use the frag API, update the
>> document about how to decide which API to use for the
>> driver author.
> 
> the fragment API
> 
>> +/**
>> + * page_pool_dev_alloc_frag() - allocate a page frag.
> 
> allocate a page fragment.
> 
> the precedent is set in
> https://www.kernel.org/doc/html/v5.0/vm/page_frags.html
> foo_frag is used in C code, and foo fragment in English docs.

Sure.

It seems I need to respin anyway as the newly merged idpf driver
from intel is also using the frag API, and removing PP_FLAG_PAGE_FRAG
flag breaks it.

And idpf driver really should be using the new API instead of
selecting which API to use according to the buf_size as below
in drivers/net/ethernet/intel/idpf/idpf_txrx.h, as it seems to
be assuming PAGE_SIZE always being 4K, and we may be able to
enable page split for buf_size > 2048 and PAGE_SIZE > 4K if using
the new API.

static inline dma_addr_t idpf_alloc_page(struct page_pool *pool,
                                         struct idpf_rx_buf *buf,
                                         unsigned int buf_size)
{
        if (buf_size == IDPF_RX_BUF_2048)
                buf->page = page_pool_dev_alloc_frag(pool, &buf->page_offset,
                                                     buf_size);
        else
                buf->page = page_pool_dev_alloc_pages(pool);

        if (!buf->page)
                return DMA_MAPPING_ERROR;

        buf->truesize = buf_size;

        return page_pool_get_dma_addr(buf->page) + buf->page_offset +
               pool->p.offset;
}

> 
> .
>