linux-kernel - Re: [PATCH v2 2/5] mm/memory_hotplug: Drop PageReserved() check in online_pages

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Message-ID: <20190814160458.GH17933@dhcp22.suse.cz>
Date:   Wed, 14 Aug 2019 18:04:58 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.de>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH v2 2/5] mm/memory_hotplug: Drop PageReserved() check in
 online_pages_range()

On Wed 14-08-19 17:41:06, David Hildenbrand wrote:
> move_pfn_range_to_zone() will set all pages to PG_reserved via
> memmap_init_zone(). The only way a page could no longer be reserved
> would be if a MEM_GOING_ONLINE notifier would clear PG_reserved - which
> is not done (the online_page callback is used for that purpose by
> e.g., Hyper-V instead). walk_system_ram_range() will never call
> online_pages_range() with duplicate PFNs, so drop the PageReserved() check.
> 
> This seems to be a leftover from ancient times where the memmap was
> initialized when adding memory and we wanted to check for already
> onlined memory.
> 
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Oscar Salvador <osalvador@...e.de>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Pavel Tatashin <pasha.tatashin@...een.com>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Signed-off-by: David Hildenbrand <david@...hat.com>

Thanks for spliting that up.
Acked-by: Michal Hocko <mhocko@...e.com>

> ---
>  mm/memory_hotplug.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 3706a137d880..10ad970f3f14 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -653,9 +653,7 @@ static int online_pages_range(unsigned long start_pfn, unsigned long nr_pages,
>  {
>  	unsigned long onlined_pages = *(unsigned long *)arg;
>  
> -	if (PageReserved(pfn_to_page(start_pfn)))
> -		onlined_pages += online_pages_blocks(start_pfn, nr_pages);
> -
> +	onlined_pages += online_pages_blocks(start_pfn, nr_pages);
>  	online_mem_sections(start_pfn, start_pfn + nr_pages);
>  
>  	*(unsigned long *)arg = onlined_pages;
> -- 
> 2.21.0
> 

-- 
Michal Hocko
SUSE Labs