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Date:   Mon, 16 Mar 2020 16:19:22 +0100
From:   Michal Hocko <mhocko@kernel.org>
To:     David Hildenbrand <david@redhat.com>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        linuxppc-dev@lists.ozlabs.org, linux-hyperv@vger.kernel.org,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Oscar Salvador <osalvador@suse.de>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Baoquan He <bhe@redhat.com>,
        Wei Yang <richard.weiyang@gmail.com>
Subject: Re: [PATCH v1 2/5] drivers/base/memory: map MMOP_OFFLINE to 0
Message-ID: <20200316151922.GT11482@dhcp22.suse.cz>
References: <20200311123026.16071-1-david@redhat.com>
 <20200311123026.16071-3-david@redhat.com>
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On Wed 11-03-20 13:30:23, David Hildenbrand wrote:
> I have no idea why we have to start at -1.

Because this is how the offline state offline was represented
originally.

> Just treat 0 as the special
> case. Clarify a comment (which was wrong, when we come via
> device_online() the first time, the online_type would have been 0 /
> MEM_ONLINE). The default is now always MMOP_OFFLINE.

git grep says that you have covered the only remaining place which
hasn't used the enum value.

> This is a preparation to use the online_type as an array index.
> 
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: "Rafael J. Wysocki" <rafael@kernel.org>
> Cc: Baoquan He <bhe@redhat.com>
> Cc: Wei Yang <richard.weiyang@gmail.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>

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

> ---
>  drivers/base/memory.c          | 11 ++++-------
>  include/linux/memory_hotplug.h |  2 +-
>  2 files changed, 5 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index 8c5ce42c0fc3..e7e77cafef80 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -211,17 +211,14 @@ static int memory_subsys_online(struct device *dev)
>  		return 0;
>  
>  	/*
> -	 * If we are called from state_store(), online_type will be
> -	 * set >= 0 Otherwise we were called from the device online
> -	 * attribute and need to set the online_type.
> +	 * When called via device_online() without configuring the online_type,
> +	 * we want to default to MMOP_ONLINE.
>  	 */
> -	if (mem->online_type < 0)
> +	if (mem->online_type == MMOP_OFFLINE)
>  		mem->online_type = MMOP_ONLINE;
>  
>  	ret = memory_block_change_state(mem, MEM_ONLINE, MEM_OFFLINE);
> -
> -	/* clear online_type */
> -	mem->online_type = -1;
> +	mem->online_type = MMOP_OFFLINE;
>  
>  	return ret;
>  }
> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
> index 261dbf010d5d..c2e06ed5e0e9 100644
> --- a/include/linux/memory_hotplug.h
> +++ b/include/linux/memory_hotplug.h
> @@ -48,7 +48,7 @@ enum {
>  /* Types for control the zone type of onlined and offlined memory */
>  enum {
>  	/* Offline the memory. */
> -	MMOP_OFFLINE = -1,
> +	MMOP_OFFLINE = 0,
>  	/* Online the memory. Zone depends, see default_zone_for_pfn(). */
>  	MMOP_ONLINE,
>  	/* Online the memory to ZONE_NORMAL. */
> -- 
> 2.24.1

-- 
Michal Hocko
SUSE Labs