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Message-ID: <c8d704f2-cc1c-52d2-3898-bf07dcb76e1a@redhat.com>
Date:   Mon, 7 Feb 2022 15:50:54 +0100
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Subject: Re: [PATCH 2/4] mm/memory_hotplug: avoid calling zone_intersects()
 for ZONE_NORMAL
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To:     Miaohe Lin <linmiaohe@huawei.com>, akpm@linux-foundation.org
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org
References: <20220207133643.23427-1-linmiaohe@huawei.com>
 <20220207133643.23427-3-linmiaohe@huawei.com>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
In-Reply-To: <20220207133643.23427-3-linmiaohe@huawei.com>
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On 07.02.22 14:36, Miaohe Lin wrote:
> If zid reaches ZONE_NORMAL, the caller will always get the NORMAL zone no
> matter what zone_intersects() returns. So we can save some possible cpu
> cycles by avoid calling zone_intersects() for ZONE_NORMAL.
> 
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
> ---
>  mm/memory_hotplug.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index cbc67c27e0dd..140809e60e9a 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -826,7 +826,7 @@ static struct zone *default_kernel_zone_for_pfn(int nid, unsigned long start_pfn
>  	struct pglist_data *pgdat = NODE_DATA(nid);
>  	int zid;
>  
> -	for (zid = 0; zid <= ZONE_NORMAL; zid++) {
> +	for (zid = 0; zid < ZONE_NORMAL; zid++) {
>  		struct zone *zone = &pgdat->node_zones[zid];
>  
>  		if (zone_intersects(zone, start_pfn, nr_pages))


Makes sense, although we just don't care about the CPU cycles at that point.

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Thanks,

David / dhildenb