linux-kernel - Re: [PATCH v2] arm64: mm: reserve hugetlb CMA after numa

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Date:   Thu, 18 Jun 2020 08:19:35 +0100
From:   Will Deacon <will@...nel.org>
To:     "Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.com>
Cc:     Roman Gushchin <guro@...com>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "nsaenzjulienne@...e.de" <nsaenzjulienne@...e.de>,
        "steve.capper@....com" <steve.capper@....com>,
        "rppt@...ux.ibm.com" <rppt@...ux.ibm.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linuxarm <linuxarm@...wei.com>,
        Matthias Brugger <matthias.bgg@...il.com>
Subject: Re: [PATCH v2] arm64: mm: reserve hugetlb CMA after numa_init

On Wed, Jun 17, 2020 at 09:43:51PM +0000, Song Bao Hua (Barry Song) wrote:
> > From: Roman Gushchin [mailto:guro@...com]
> > On Wed, Jun 17, 2020 at 11:38:03AM +0000, Song Bao Hua (Barry Song)
> > > > From: Will Deacon [mailto:will@...nel.org]
> > > > 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
> > > > > 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.

Maybe one for RaspberryPi 5, huh? ;)

But ok, I'll take your patch as-is and add a comment about NUMA.

Thanks,

Will