netdev - Re: [PATCH net-next RFC 1/2] page_pool: add page recycling support based on elevated refcnt

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Message-ID: <ec994486-b385-0597-39f7-128092cba0ce@huawei.com>
Date:   Fri, 2 Jul 2021 18:15:13 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     Jesper Dangaard Brouer <jbrouer@...hat.com>, <davem@...emloft.net>,
        <kuba@...nel.org>
CC:     <linuxarm@...neuler.org>, <yisen.zhuang@...wei.com>,
        <salil.mehta@...wei.com>, <thomas.petazzoni@...tlin.com>,
        <mw@...ihalf.com>, <linux@...linux.org.uk>, <hawk@...nel.org>,
        <ilias.apalodimas@...aro.org>, <ast@...nel.org>,
        <daniel@...earbox.net>, <john.fastabend@...il.com>,
        <akpm@...ux-foundation.org>, <peterz@...radead.org>,
        <will@...nel.org>, <willy@...radead.org>, <vbabka@...e.cz>,
        <fenghua.yu@...el.com>, <guro@...com>, <peterx@...hat.com>,
        <feng.tang@...el.com>, <jgg@...pe.ca>, <mcroce@...rosoft.com>,
        <hughd@...gle.com>, <jonathan.lemon@...il.com>, <alobakin@...me>,
        <willemb@...gle.com>, <wenxu@...oud.cn>, <cong.wang@...edance.com>,
        <haokexin@...il.com>, <nogikh@...gle.com>, <elver@...gle.com>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <bpf@...r.kernel.org>, Alexander Duyck <alexander.duyck@...il.com>
Subject: Re: [PATCH net-next RFC 1/2] page_pool: add page recycling support
 based on elevated refcnt

On 2021/7/2 17:42, Jesper Dangaard Brouer wrote:
> 
> On 30/06/2021 11.17, Yunsheng Lin wrote:
>> Currently page pool only support page recycling only when
>> refcnt of page is one, which means it can not support the
>> split page recycling implemented in the most ethernet driver.
> 
> Cc. Alex Duyck as I consider him an expert in this area.

Thanks.

> 
> 
>> So add elevated refcnt support in page pool, and support
>> allocating page frag to enable multi-frames-per-page based
>> on the elevated refcnt support.
>>
>> As the elevated refcnt is per page, and there is no space
>> for that in "struct page" now, so add a dynamically allocated
>> "struct page_pool_info" to record page pool ptr and refcnt
>> corrsponding to a page for now. Later, we can recycle the
>> "struct page_pool_info" too, or use part of page memory to
>> record pp_info.
> 
> I'm not happy with allocating a memory (slab) object "struct page_pool_info" per page.
> 
> This also gives us an extra level of indirection.

I'm not happy with that either, if there is better way to
avoid that, I will be happy to change it:)

> 
> 
> You are also adding a page "frag" API inside page pool, which I'm not 100% convinced belongs inside page_pool APIs.
> 
> Please notice the APIs that Alex Duyck added in mm/page_alloc.c:

Actually, that is where the idea of using "page frag" come from.

Aside from the performance improvement, there is memory usage
decrease for 64K page size kernel, which means a 64K page can
be used by 32 description with 2k buffer size, and that is a
lot of memory saving for 64 page size kernel comparing to the
current split page reusing implemented in the driver.


> 
>  __page_frag_cache_refill() + __page_frag_cache_drain() + page_frag_alloc_align()
> 
> 

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