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Subject: Re: [PATCH 1/4] mm/page_alloc: always initialize memory map for the
 holes
To:     Mike Rapoport <rppt@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     Michal Simek <monstr@monstr.eu>,
        Mike Rapoport <rppt@linux.ibm.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
References: <20210714123739.16493-1-rppt@kernel.org>
 <20210714123739.16493-2-rppt@kernel.org>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
Message-ID: <175e0e1e-90cd-5c69-69a3-9f44462679e3@redhat.com>
Date:   Wed, 25 Aug 2021 14:11:23 +0200
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On 14.07.21 14:37, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@linux.ibm.com>
> 
> Currently memory map for the holes is initialized only when SPARSEMEM
> memory model is used. Yet, even with FLATMEM there could be holes in the
> physical memory layout that have memory map entries.
> 
> For instance, the memory reserved using e820 API on i386 or
> "reserved-memory" nodes in device tree would not appear in memblock.memory
> and hence the struct pages for such holes will be skipped during memory map
> initialization.
> 
> These struct pages will be zeroed because the memory map for FLATMEM
> systems is allocated with memblock_alloc_node() that clears the allocated
> memory. While zeroed struct pages do not cause immediate problems, the
> correct behaviour is to initialize every page using __init_single_page().
> Besides, enabling page poison for FLATMEM case will trigger
> PF_POISONED_CHECK() unless the memory map is properly initialized.
> 
> Make sure init_unavailable_range() is called for both SPARSEMEM and FLATMEM
> so that struct pages representing memory holes would appear as PG_Reserved
> with any memory layout.
> 
> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
> ---
>   mm/page_alloc.c | 8 --------
>   1 file changed, 8 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 3b97e17806be..878d7af4403d 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -6624,7 +6624,6 @@ static void __meminit zone_init_free_lists(struct zone *zone)
>   	}
>   }
>   
> -#if !defined(CONFIG_FLATMEM)
>   /*
>    * Only struct pages that correspond to ranges defined by memblock.memory
>    * are zeroed and initialized by going through __init_single_page() during
> @@ -6669,13 +6668,6 @@ static void __init init_unavailable_range(unsigned long spfn,
>   		pr_info("On node %d, zone %s: %lld pages in unavailable ranges",
>   			node, zone_names[zone], pgcnt);
>   }
> -#else
> -static inline void init_unavailable_range(unsigned long spfn,
> -					  unsigned long epfn,
> -					  int zone, int node)
> -{
> -}
> -#endif
>   
>   static void __init memmap_init_zone_range(struct zone *zone,
>   					  unsigned long start_pfn,
> 

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Thanks,

David / dhildenb