linux-kernel - Re: [PATCH v5 RFC 1/6] page_pool: frag API support for 32-bit arch with 64-bit DMA

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Date:   Wed, 12 Jul 2023 20:34:12 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     Alexander Lobakin <aleksander.lobakin@...el.com>,
        Jakub Kicinski <kuba@...nel.org>
CC:     Yunsheng Lin <yunshenglin0825@...il.com>, <davem@...emloft.net>,
        <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>,
        Saeed Mahameed <saeedm@...dia.com>,
        Leon Romanovsky <leon@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        <linux-rdma@...r.kernel.org>
Subject: Re: [PATCH v5 RFC 1/6] page_pool: frag API support for 32-bit arch
 with 64-bit DMA

On 2023/7/12 0:59, Alexander Lobakin wrote:
> From: Jakub Kicinski <kuba@...nel.org>
> Date: Tue, 11 Jul 2023 09:37:05 -0700
> 
>> On Tue, 11 Jul 2023 12:59:00 +0200 Alexander Lobakin wrote:
>>> I'm fine with that, although ain't really able to work on this myself
>>> now :s (BTW I almost finished Netlink bigints, just some more libie/IAVF
>>> crap).
>>
>> FWIW I was thinking about the bigints recently, and from ynl
>> perspective I think we may want two flavors :( One which is at
>> most the length of platform's long long, and another which is
> 
> (not sure we shouldn't split a separate thread off this one at this
>  point :D)
> 
> `long long` or `long`? `long long` is always 64-bit unless I'm missing
> something. On my 32-bit MIPS they were :D
> If `long long`, what's the point then if we have %NLA_U64 and would
> still have to add dumb padding attrs? :D I thought the idea was to carry
> 64+ bits encapsulated in 32-bit primitives.
> 
>> always a bigint. The latter will be more work for user space
>> to handle, so given 99% of use cases don't need more than 64b
>> we should make its life easier?
>>
>>> It just needs to be carefully designed, because if we want move ALL the
>>> inlines to a new header, we may end up including 2 PP's headers in each
>>> file. That's why I'd prefer "core/driver" separation. Let's say skbuff.c
>>> doesn't need page_pool_create(), page_pool_alloc(), and so on, while
>>> drivers don't need some of its internal functions.
>>> OTOH after my patch it's included in only around 20-30 files on
>>> allmodconfig. That is literally nothing comparing to e.g. kernel.h
>>> (w/includes) :D
>>
>> Well, once you have to rebuilding 100+ files it gets pretty hard to
>> clean things up ;) 
>>
>> I think I described the preferred setup, previously:
>>
>> $path/page_pool.h:
>>
>> #include <$path/page_pool/types.h>
>> #include <$path/page_pool/helpers.h>
>>
>> $path/page_pool/types.h - has types
>> $path/page_pool/helpers.h - has all the inlines
>>
>> C sources can include $path/page_pool.h, headers should generally only
>> include $path/page_pool/types.h.

Does spliting the page_pool.h as above fix the problem about including
a ton of static inline functions from "linux/dma-mapping.h" in skbuff.c?

As the $path/page_pool/helpers.h which uses dma_get_cache_alignment()
must include the "linux/dma-mapping.h" which has dma_get_cache_alignment()
defining as a static inline function.
and if skbuff.c include $path/page_pool.h or $path/page_pool/helpers.h,
doesn't we still have the same problem? Or do I misunderstand something
here?

> 
> Aaah okay, I did read it backwards ._. Moreover, generic stack barely
> uses PP's inlines, it needs externals mostly.
> 
> Thanks,
> Olek
> 
> .
>