linux-kernel - Re: [PATCH 5/9] mm, memory_hotplug: remove explicit build_all_zonelists from try_online

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Date:   Thu, 20 Jul 2017 08:13:16 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Michal Hocko <mhocko@...nel.org>, linux-mm@...ck.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>,
        Johannes Weiner <hannes@...xchg.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...e.com>, Toshi Kani <toshi.kani@...com>
Subject: Re: [PATCH 5/9] mm, memory_hotplug: remove explicit
 build_all_zonelists from try_online_node

On 07/14/2017 10:00 AM, Michal Hocko wrote:
> From: Michal Hocko <mhocko@...e.com>
> 
> try_online_node calls hotadd_new_pgdat which already calls
> build_all_zonelists. So the additional call is redundant.  Even though
> hotadd_new_pgdat will only initialize zonelists of the new node this is
> the right thing to do because such a node doesn't have any memory so
> other zonelists would ignore all the zones from this node anyway.

Doesn't the "if (pgdat<...>zone == NULL) in fact mean, that this is just
always dead code? Even more reason to remove it.

> Cc: Toshi Kani <toshi.kani@...com>
> Signed-off-by: Michal Hocko <mhocko@...e.com>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

> ---
>  mm/memory_hotplug.c | 7 -------
>  1 file changed, 7 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 639b8af37c45..0d2f6a11075c 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1104,13 +1104,6 @@ int try_online_node(int nid)
>  	node_set_online(nid);
>  	ret = register_one_node(nid);
>  	BUG_ON(ret);
> -
> -	if (pgdat->node_zonelists->_zonerefs->zone == NULL) {
> -		mutex_lock(&zonelists_mutex);
> -		build_all_zonelists(NULL);
> -		mutex_unlock(&zonelists_mutex);
> -	}
> -
>  out:
>  	mem_hotplug_done();
>  	return ret;
>