RE: [PATCH v2] arm64: mm: reserve hugetlb CMA after numa_init

["Song Bao Hua (Barry Song)" <song.bao.hua@hisilicon.com>]

> -----Original Message-----
> From: Roman Gushchin [mailto:guro@fb.com]
> Sent: Thursday, June 18, 2020 6:20 AM
> To: Song Bao Hua (Barry Song) <song.bao.hua@hisilicon.com>
> Cc: Will Deacon <will@kernel.org>; catalin.marinas@arm.com;
> nsaenzjulienne@suse.de; steve.capper@arm.com; rppt@linux.ibm.com;
> akpm@linux-foundation.org; linux-arm-kernel@lists.infradead.org;
> linux-kernel@vger.kernel.org; Linuxarm <linuxarm@huawei.com>; Matthias
> Brugger <matthias.bgg@gmail.com>
> Subject: Re: [PATCH v2] arm64: mm: reserve hugetlb CMA after numa_init
> 
> On Wed, Jun 17, 2020 at 11:38:03AM +0000, Song Bao Hua (Barry Song)
> wrote:
> >
> >
> > > -----Original Message-----
> > > From: Will Deacon [mailto:will@kernel.org]
> > > Sent: Wednesday, June 17, 2020 10:18 PM
> > > To: Song Bao Hua (Barry Song) <song.bao.hua@hisilicon.com>
> > > Cc: catalin.marinas@arm.com; nsaenzjulienne@suse.de;
> > > steve.capper@arm.com; rppt@linux.ibm.com;
> akpm@linux-foundation.org;
> > > linux-arm-kernel@lists.infradead.org; linux-kernel@vger.kernel.org;
> Linuxarm
> > > <linuxarm@huawei.com>; Matthias Brugger <matthias.bgg@gmail.com>;
> > > Roman Gushchin <guro@fb.com>
> > > Subject: Re: [PATCH v2] arm64: mm: reserve hugetlb CMA after numa_init
> > >
> > > On Wed, Jun 17, 2020 at 10:19:24AM +1200, Barry Song wrote:
> > > > hugetlb_cma_reserve() is called at the wrong place. numa_init has not
> been
> > > > done yet. so all reserved memory will be located at node0.
> > > >
> > > > Fixes: cf11e85fc08c ("mm: hugetlb: optionally allocate gigantic
> hugepages
> > > using cma")
> > >
> > > Damn, wasn't CC'd on that :/
> > >
> > > > Cc: Matthias Brugger <matthias.bgg@gmail.com>
> > > > Acked-by: Roman Gushchin <guro@fb.com>
> > > > Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
> > > > ---
> > > >  -v2: add Fixes tag according to Matthias Brugger's comment
> > > >
> > > >  arch/arm64/mm/init.c | 10 +++++-----
> > > >  1 file changed, 5 insertions(+), 5 deletions(-)
> > > >
> > > > diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> > > > index e631e6425165..41914b483d54 100644
> > > > --- a/arch/arm64/mm/init.c
> > > > +++ b/arch/arm64/mm/init.c
> > > > @@ -404,11 +404,6 @@ void __init arm64_memblock_init(void)
> > > >  	high_memory = __va(memblock_end_of_DRAM() - 1) + 1;
> > > >
> > > >  	dma_contiguous_reserve(arm64_dma32_phys_limit);
> > > > -
> > > > -#ifdef CONFIG_ARM64_4K_PAGES
> > > > -	hugetlb_cma_reserve(PUD_SHIFT - PAGE_SHIFT);
> > > > -#endif
> > >
> > > Why is this dependent on CONFIG_ARM64_4K_PAGES? We unconditionally
> > > select ARCH_HAS_GIGANTIC_PAGE so this seems unnecessary.
> >
> > Roman, would you like to answer this question? Have you found any
> problem if system
> > doesn't set 4K_PAGES?
> 
> No, I was just following the code in arch/arm64/mm/hugetlbpage.c where all
> related to PUD-sized pages is guarded by CONFIG_ARM64_4K_PAGES.
> Actually I did all my testing on x86-64, I don't even have any arm hardware.
> 
> I'm totally fine with removing this #ifdef if it's not needed.

At this moment, I would suggest we should keep this "ifdef". Otherwise, hugetlb_cma_reserve() won't be really useful.

For example, while setting PAGE size to 64KB. I got this error in hugetlb_cma_reserve():
hugetlb_cma: cma area should be at least 4194304 MiB
This is absolutely unreasonable.

Supporting hugetlb_cma_reserve() for page sizes other than 4k is a different issue. 
It might be addressed in a separate patch later.

> 
> Thanks!
> 
> >
> > >
> > > > -
> > > >  }
> > > >
> > > >  void __init bootmem_init(void)
> > > > @@ -424,6 +419,11 @@ void __init bootmem_init(void)
> > > >  	min_low_pfn = min;
> > > >
> > > >  	arm64_numa_init();
> > > > +
> > > > +#ifdef CONFIG_ARM64_4K_PAGES
> > > > +	hugetlb_cma_reserve(PUD_SHIFT - PAGE_SHIFT);
> > > > +#endif
> > >
> > > A comment here wouldn't hurt, as it does look a lot more natural next
> > > to dma_contiguous_reserve().
> >
> > Will add some comment here.
> >
> > >
> > > Will
> >
> > barry

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