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

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Date: Tue, 11 Jul 2023 18:59:51 +0200
From: Alexander Lobakin <aleksander.lobakin@...el.com>
To: Jakub Kicinski <kuba@...nel.org>
CC: Yunsheng Lin <yunshenglin0825@...il.com>, Yunsheng Lin
	<linyunsheng@...wei.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

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.

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

Thanks,
Olek