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

[Alexander Duyck <alexander.duyck@gmail.com>]

On Mon, Jul 8, 2024 at 11:58 PM Yunsheng Lin <linyunsheng@huawei.com> wrote:
>
> On 2024/7/8 22:30, Alexander Duyck wrote:
> > On Mon, Jul 8, 2024 at 3:58 AM Yunsheng Lin <linyunsheng@huawei.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/

The point is you need to avoid pulling mm.h into sched.h. To do that
you have to pull the data structure out and place it in a different
header file. So maybe instead of creating yet another header file you
can just place the structure in mm_types_task.h and once you have
dealt with all of the other users you can finally drop the page_frag
structure.