Re: [PATCH] mm: Fix for PG_reserved page flag clearing

[Michal Hocko <mhocko@suse.com>]

On Mon 19-02-18 12:06:14, Masayoshi Mizuma wrote:
> From: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
> 
> struct page is inizialized as zero in __init_single_page().
> If the page is offlined page, PG_reserved flag is set in early boot
> time before __init_single_page(), so we should not clear the flag.
> 
> The real problem is that we can not online the offlined page
> through following sysfs operation because offlined page is
> expected PG_reserved flag is set. 
> It is not needed the initialization, so remove it simply.
> 
>   Code:
> 
>   static int online_pages_range(unsigned long start_pfn, 
>   ...
>           if (PageReserved(pfn_to_page(start_pfn))) <= HERE!!
>                   for (i = 0; i < nr_pages; i++) {
>                           page = pfn_to_page(start_pfn + i);
>                           (*online_page_callback)(page);
>                           onlined_pages++;
>   sysfs operation:
> 
>   # echo online > /sys/devices/system/node/node2/memory12288/online
>   # cat /sys/devices/system/node/node2/memory12288/online 
>   1
>   # cat /sys/devices/system/node/node2/meminfo 
>   Node 2 MemTotal:              0 kB

Nack. The patch is simply wrong. We do need to zero page for the boot
pages. I believe the fix you are looking for is 9bb5a391f9a5 ("mm,
memory_hotplug: fix memmap initialization"). Or do you still see a
problem with this patch applied?

> Fixes: f7f99100d8d9 ("mm: stop zeroing memory during allocation in vmemmap")
> Signed-off-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
> ---
>  mm/page_alloc.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 76c9688..3260cd2 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1179,7 +1179,6 @@ static void free_one_page(struct zone *zone,
>  static void __meminit __init_single_page(struct page *page, unsigned long pfn,
>  				unsigned long zone, int nid)
>  {
> -	mm_zero_struct_page(page);
>  	set_page_links(page, zone, nid, pfn);
>  	init_page_count(page);
>  	page_mapcount_reset(page);
> -- 
> 2.16.1
> 
> - Masayoshi

-- 
Michal Hocko
SUSE Labs

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