linux-kernel - Re: [PATCH v1 4/4] mm/memory_hotplug: online_pages cannot be 0 in online

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Date:   Wed, 14 Aug 2019 16:26:13 +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 v1 4/4] mm/memory_hotplug: online_pages cannot be 0 in
 online_pages()

On Fri 09-08-19 14:57:01, David Hildenbrand wrote:
> walk_system_ram_range() will fail with -EINVAL in case
> online_pages_range() was never called (== no resource applicable in the
> range). Otherwise, we will always call online_pages_range() with
> nr_pages > 0 and, therefore, have online_pages > 0.

I have no idea why those checks where there TBH. Tried to dig out
commits which added them but didn't help.

> Remove that special handling.
> 
> 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>

Acked-by: Michal Hocko <mhocko@...e.com>

> ---
>  mm/memory_hotplug.c | 22 +++++++++-------------
>  1 file changed, 9 insertions(+), 13 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 87f85597a19e..07e72fe17495 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -854,6 +854,7 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ
>  	ret = walk_system_ram_range(pfn, nr_pages, &onlined_pages,
>  		online_pages_range);
>  	if (ret) {
> +		/* not a single memory resource was applicable */
>  		if (need_zonelists_rebuild)
>  			zone_pcp_reset(zone);
>  		goto failed_addition;
> @@ -867,27 +868,22 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ
>  
>  	shuffle_zone(zone);
>  
> -	if (onlined_pages) {
> -		node_states_set_node(nid, &arg);
> -		if (need_zonelists_rebuild)
> -			build_all_zonelists(NULL);
> -		else
> -			zone_pcp_update(zone);
> -	}
> +	node_states_set_node(nid, &arg);
> +	if (need_zonelists_rebuild)
> +		build_all_zonelists(NULL);
> +	else
> +		zone_pcp_update(zone);
>  
>  	init_per_zone_wmark_min();
>  
> -	if (onlined_pages) {
> -		kswapd_run(nid);
> -		kcompactd_run(nid);
> -	}
> +	kswapd_run(nid);
> +	kcompactd_run(nid);
>  
>  	vm_total_pages = nr_free_pagecache_pages();
>  
>  	writeback_set_ratelimit();
>  
> -	if (onlined_pages)
> -		memory_notify(MEM_ONLINE, &arg);
> +	memory_notify(MEM_ONLINE, &arg);
>  	mem_hotplug_done();
>  	return 0;
>  
> -- 
> 2.21.0

-- 
Michal Hocko
SUSE Labs