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Date: Sun, 21 Jan 2018 17:21:56 -0800
From: Matthew Wilcox <willy@infradead.org>
To: Eugeniu Rosca <erosca@de.adit-jv.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@suse.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
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        AKASHI Takahiro <takahiro.akashi@linaro.org>,
        Pavel Tatashin <pasha.tatashin@oracle.com>,
        Gioh Kim <gi-oh.kim@profitbricks.com>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        Wei Yang <richard.weiyang@gmail.com>,
        Miles Chen <miles.chen@mediatek.com>, Vlastimil Babka <vbabka@suse.cz>,
        Mel Gorman <mgorman@suse.de>, Hillf Danton <hillf.zj@alibaba-inc.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Paul Burton <paul.burton@mips.com>,
        James Hartley <james.hartley@mips.com>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [PATCH v2 1/1] mm: page_alloc: skip over regions of invalid pfns
 on UMA
Message-ID: <20180122012156.GA10428@bombadil.infradead.org>
References: <20180121144753.3109-1-erosca@de.adit-jv.com>
 <20180121144753.3109-2-erosca@de.adit-jv.com>
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I like the patch.  I think it could be better.

> +++ b/mm/page_alloc.c
> @@ -5344,7 +5344,7 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
>  			goto not_early;
>  
>  		if (!early_pfn_valid(pfn)) {
> -#ifdef CONFIG_HAVE_MEMBLOCK_NODE_MAP
> +#ifdef CONFIG_HAVE_MEMBLOCK
>  			/*
>  			 * Skip to the pfn preceding the next valid one (or
>  			 * end_pfn), such that we hit a valid pfn (or end_pfn)

This ifdef makes me sad.  Here's more of the context:

                if (!early_pfn_valid(pfn)) {
#ifdef CONFIG_HAVE_MEMBLOCK_NODE_MAP
                        /*
                         * Skip to the pfn preceding the next valid one (or
                         * end_pfn), such that we hit a valid pfn (or end_pfn)
                         * on our next iteration of the loop.
                         */
                        pfn = memblock_next_valid_pfn(pfn, end_pfn) - 1;
#endif
                        continue;
                }

This is crying out for:

#ifdef CONFIG_HAVE_MEMBLOCK
unsigned long memblock_next_valid_pfn(unsigned long pfn, unsigned long max_pfn);
#else
static inline unsigned long memblock_next_valid_pfn(unsigned long pfn,
		unsigned long max_pfn)
{
	return pfn + 1;
}
#endif

in a header file somewhere.