linux-kernel - Re: [PATCH 2/5] mm/memory_hotplug: Avoid node_set/clear_state(N_HIGH_MEMORY) when !CONFIG

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Date:   Thu, 20 Sep 2018 20:59:18 +0000
From:   Pasha Tatashin <Pavel.Tatashin@...rosoft.com>
To:     Oscar Salvador <osalvador@...hadventures.net>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
CC:     "mhocko@...e.com" <mhocko@...e.com>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "david@...hat.com" <david@...hat.com>,
        "Jonathan.Cameron@...wei.com" <Jonathan.Cameron@...wei.com>,
        "yasu.isimatu@...il.com" <yasu.isimatu@...il.com>,
        "malat@...ian.org" <malat@...ian.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Oscar Salvador <osalvador@...e.de>
Subject: Re: [PATCH 2/5] mm/memory_hotplug: Avoid
 node_set/clear_state(N_HIGH_MEMORY) when !CONFIG_HIGHMEM



On 9/19/18 6:08 AM, Oscar Salvador wrote:
> From: Oscar Salvador <osalvador@...e.de>
> 
> Currently, when !CONFIG_HIGHMEM, status_change_nid_high is being set
> to status_change_nid_normal, but on such systems N_HIGH_MEMORY falls
> back to N_NORMAL_MEMORY.
> That means that if status_change_nid_normal is not -1,
> we will perform two calls to node_set_state for the same memory type.
> 
> Set status_change_nid_high to -1 for !CONFIG_HIGHMEM, so we skip the
> double call in node_states_set_node.
> 
> The same goes for node_clear_state.
> 
> Signed-off-by: Oscar Salvador <osalvador@...e.de>

Reviewed-by: Pavel Tatashin <pavel.tatashin@...rosoft.com>

This is a rare case where I think comments are unnecessary as the code
is self explanatory. So, I would remove the comments before:

> +	arg->status_change_nid_high = -1;

Pavel

> ---
>  mm/memory_hotplug.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 63facfc57224..c2c7359bd0a7 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -731,7 +731,11 @@ static void node_states_check_changes_online(unsigned long nr_pages,
>  	else
>  		arg->status_change_nid_high = -1;
>  #else
> -	arg->status_change_nid_high = arg->status_change_nid_normal;
> +	/*
> +	 * When !CONFIG_HIGHMEM, N_HIGH_MEMORY equals N_NORMAL_MEMORY
> +	 * so setting the node for N_NORMAL_MEMORY is enough.
> +	 */
> +	arg->status_change_nid_high = -1;
>  #endif
>  
>  	/*
> @@ -1555,7 +1559,11 @@ static void node_states_check_changes_offline(unsigned long nr_pages,
>  	else
>  		arg->status_change_nid_high = -1;
>  #else
> -	arg->status_change_nid_high = arg->status_change_nid_normal;
> +	/*
> +	 * When !CONFIG_HIGHMEM, N_HIGH_MEMORY equals N_NORMAL_MEMORY
> +	 * so clearing the node for N_NORMAL_MEMORY is enough.
> +	 */
> +	arg->status_change_nid_high = -1;
>  #endif
>  
>  	/*
>