linux-kernel - Re: [PATCH v3 1/1] mm: page_alloc: skip over regions of invalid pfns on UMA

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Date:   Mon, 29 Jan 2018 19:47:46 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Eugeniu Rosca <erosca@...adit-jv.com>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        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>,
        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 v3 1/1] mm: page_alloc: skip over regions of invalid pfns
 on UMA

On Wed 24-01-18 15:35:45, Eugeniu Rosca wrote:
[...]
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 76c9688b6a0a..4a3d5936a9a0 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5344,14 +5344,12 @@ 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
>  			/*
>  			 * 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;

Wouldn't it be just simpler to have ifdef CONFIG_HAVE_MEMBLOCK rather
than define memblock_next_valid_pfn for !HAVE_MEMBLOCK and then do the
(pfn + 1 ) - 1 games. I am usually against ifdefs in the code but that
would require a larger surgery to memmap_init_zone.

To be completely honest, I would like to see HAVE_MEMBLOCK_NODE_MAP
gone.

Other than that, the patch looks sane to me.

>  		}
>  		if (!early_pfn_in_nid(pfn, nid))
> -- 
> 2.15.1
> 

-- 
Michal Hocko
SUSE Labs