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Date:   Fri, 25 Jan 2019 21:32:52 +0200
From:   Mike Rapoport <rppt@linux.ibm.com>
To:     Catalin Marinas <catalin.marinas@arm.com>
Cc:     linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
        Christoph Hellwig <hch@lst.de>,
        "David S. Miller" <davem@davemloft.net>,
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        Greentime Hu <green.hu@gmail.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Guan Xuetao <gxt@pku.edu.cn>, Guo Ren <guoren@kernel.org>,
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Subject: Re: [PATCH v2 06/21] memblock: memblock_phys_alloc_try_nid(): don't
 panic
References: <1548057848-15136-1-git-send-email-rppt@linux.ibm.com>
 <1548057848-15136-7-git-send-email-rppt@linux.ibm.com>
 <20190125174502.GL25901@arrakis.emea.arm.com>
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On Fri, Jan 25, 2019 at 05:45:02PM +0000, Catalin Marinas wrote:
> On Mon, Jan 21, 2019 at 10:03:53AM +0200, Mike Rapoport wrote:
> > diff --git a/arch/arm64/mm/numa.c b/arch/arm64/mm/numa.c
> > index ae34e3a..2c61ea4 100644
> > --- a/arch/arm64/mm/numa.c
> > +++ b/arch/arm64/mm/numa.c
> > @@ -237,6 +237,10 @@ static void __init setup_node_data(int nid, u64 start_pfn, u64 end_pfn)
> >  		pr_info("Initmem setup node %d [<memory-less node>]\n", nid);
> >  
> >  	nd_pa = memblock_phys_alloc_try_nid(nd_size, SMP_CACHE_BYTES, nid);
> > +	if (!nd_pa)
> > +		panic("Cannot allocate %zu bytes for node %d data\n",
> > +		      nd_size, nid);
> > +
> >  	nd = __va(nd_pa);
> >  
> >  	/* report and initialize */
> 
> Does it mean that memblock_phys_alloc_try_nid() never returns valid
> physical memory starting at 0?

Yes, it does.
memblock_find_in_range_node() that is used by all allocation methods
skips the first page [1].
 
[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/mm/memblock.c#n257

> -- 
> Catalin
> 

-- 
Sincerely yours,
Mike.