linux-kernel - Re: [PATCH v2 1/1] mm: page_alloc: skip over regions of invalid pfns on UMA

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Date:   Sun, 21 Jan 2018 17:21:56 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Eugeniu Rosca <erosca@...adit-jv.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Steven Sistare <steven.sistare@...cle.com>,
        AKASHI Takahiro <takahiro.akashi@...aro.org>,
        Pavel Tatashin <pasha.tatashin@...cle.com>,
        Gioh Kim <gi-oh.kim@...fitbricks.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Wei Yang <richard.weiyang@...il.com>,
        Miles Chen <miles.chen@...iatek.com>,
        Vlastimil Babka <vbabka@...e.cz>, Mel Gorman <mgorman@...e.de>,
        Hillf Danton <hillf.zj@...baba-inc.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Paul Burton <paul.burton@...s.com>,
        James Hartley <james.hartley@...s.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2 1/1] mm: page_alloc: skip over regions of invalid pfns
 on UMA


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.