linux-kernel - Re: [PATCH net-next v9 10/13] mm: page_frag: introduce prepare/probe/commit API

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Message-ID: <2b7ecaca-9a17-e057-8897-d0684b31591d@huawei.com>
Date: Tue, 9 Jul 2024 14:57:59 +0800
From: Yunsheng Lin <linyunsheng@...wei.com>
To: Alexander Duyck <alexander.duyck@...il.com>
CC: Yunsheng Lin <yunshenglin0825@...il.com>, <davem@...emloft.net>,
	<kuba@...nel.org>, <pabeni@...hat.com>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Andrew Morton <akpm@...ux-foundation.org>,
	<linux-mm@...ck.org>
Subject: Re: [PATCH net-next v9 10/13] mm: page_frag: introduce
 prepare/probe/commit API

On 2024/7/8 22:30, Alexander Duyck wrote:
> On Mon, Jul 8, 2024 at 3:58 AM Yunsheng Lin <linyunsheng@...wei.com> wrote:
>>
>> On 2024/7/8 1:12, Alexander Duyck wrote:
>>
>> ...
>>
>>> The issue is the dependency mess that has been created with patch 11
>>> in the set. Again you are conflating patches which makes this really
>>> hard to debug or discuss as I make suggestions on one patch and you
>>> claim it breaks things that are really due to issues in another patch.
>>> So the issue is you included this header into include/linux/sched.h
>>> which is included in linux/mm_types.h. So what happens then is that
>>> you have to include page_frag_cache.h *before* you can include the
>>> bits from mm_types.h
>>>
>>> What might make more sense to solve this is to look at just moving the
>>> page_frag_cache into mm_types_task.h and then having it replace the
>>> page_frag struct there since mm_types.h will pull that in anyway. That
>>> way sched.h can avoid having to pull in page_frag_cache.h.
>>
>> It seems the above didn't work either, as asm-offsets.c does depend on
>> mm_types_task.h too.
>>
>> In file included from ./include/linux/mm.h:16,
>>                  from ./include/linux/page_frag_cache.h:10,
>>                  from ./include/linux/mm_types_task.h:11,
>>                  from ./include/linux/mm_types.h:5,
>>                  from ./include/linux/mmzone.h:22,
>>                  from ./include/linux/gfp.h:7,
>>                  from ./include/linux/slab.h:16,
>>                  from ./include/linux/resource_ext.h:11,
>>                  from ./include/linux/acpi.h:13,
>>                  from ./include/acpi/apei.h:9,
>>                  from ./include/acpi/ghes.h:5,
>>                  from ./include/linux/arm_sdei.h:8,
>>                  from arch/arm64/kernel/asm-offsets.c:10:
>> ./include/linux/mmap_lock.h: In function ‘mmap_assert_locked’:
>> ./include/linux/mmap_lock.h:65:23: error: invalid use of undefined type ‘const struct mm_struct’
>>    65 |  rwsem_assert_held(&mm->mmap_lock);
> 
> Do not include page_frag_cache.h in mm_types_task.h. Just move the
> struct page_frag_cache there to replace struct page_frag.

The above does seem a clever idea, but doesn't doing above also seem to
defeat some purpose of patch 1? Anyway, it seems workable for trying
to avoid adding a new header for a single struct.

About the 'replace' part, as mentioned in [1], the 'struct page_frag'
is still needed as this patchset is large enough that replacing is only
done for sk_page_frag(), there are still other places using page_frag
that can be replaced by page_frag_cache in the following patchset.

1. https://lore.kernel.org/all/b200a609-2f30-ec37-39b6-f37ed8092f41@huawei.com/

> .
>