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Date:   Mon, 24 Apr 2023 04:50:37 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Yajun Deng <yajun.deng@linux.dev>
Cc:     david@redhat.com, osalvador@suse.de, gregkh@linuxfoundation.org,
        rafael@kernel.org, akpm@linux-foundation.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH] mmzone: Introduce for_each_populated_zone_pgdat()
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References: <20230424030756.1795926-1-yajun.deng@linux.dev>
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On Mon, Apr 24, 2023 at 11:07:56AM +0800, Yajun Deng wrote:
> Instead of define an index and determining if the zone has memory,
> introduce for_each_populated_zone_pgdat() helper that can be used
> to iterate over each populated zone in pgdat, and convert the most
> obvious users to it.

I don't think the complexity of the helper justifies the simplification
of the users.

> +++ b/include/linux/mmzone.h
> @@ -1580,6 +1580,14 @@ extern struct zone *next_zone(struct zone *zone);
>  			; /* do nothing */		\
>  		else
>  
> +#define for_each_populated_zone_pgdat(zone, pgdat, max) \
> +	for (zone = pgdat->node_zones;                  \
> +	     zone < pgdat->node_zones + max;            \
> +	     zone++)                                    \
> +		if (!populated_zone(zone))		\
> +			; /* do nothing */		\
> +		else
> +