linux-kernel - Re: [PATCH v6 3/6] mm/cma: populate ZONE

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Date:   Tue, 18 Oct 2016 09:42:57 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     js1304@...il.com, Andrew Morton <akpm@...ux-foundation.org>
Cc:     Rik van Riel <riel@...hat.com>,
        Johannes Weiner <hannes@...xchg.org>,
        mgorman@...hsingularity.net, Laura Abbott <lauraa@...eaurora.org>,
        Minchan Kim <minchan@...nel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Michal Nazarewicz <mina86@...a86.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v6 3/6] mm/cma: populate ZONE_CMA

On 10/14/2016 05:03 AM, js1304@...il.com wrote:
> @@ -145,6 +145,35 @@ static int __init cma_activate_area(struct cma *cma)
>  static int __init cma_init_reserved_areas(void)
>  {
>  	int i;
> +	struct zone *zone;
> +	pg_data_t *pgdat;
> +
> +	if (!cma_area_count)
> +		return 0;
> +
> +	for_each_online_pgdat(pgdat) {
> +		unsigned long start_pfn = UINT_MAX, end_pfn = 0;
> +
> +		for (i = 0; i < cma_area_count; i++) {
> +			if (pfn_to_nid(cma_areas[i].base_pfn) !=
> +				pgdat->node_id)
> +				continue;
> +
> +			start_pfn = min(start_pfn, cma_areas[i].base_pfn);
> +			end_pfn = max(end_pfn, cma_areas[i].base_pfn +
> +						cma_areas[i].count);
> +		}
> +
> +		if (!end_pfn)
> +			continue;
> +
> +		zone = &pgdat->node_zones[ZONE_CMA];
> +
> +		/* ZONE_CMA doesn't need to exceed CMA region */
> +		zone->zone_start_pfn = max(zone->zone_start_pfn, start_pfn);
> +		zone->spanned_pages = min(zone_end_pfn(zone), end_pfn) -
> +					zone->zone_start_pfn;

Hmm, do the max/min here work as intended? IIUC the initial 
zone_start_pfn is UINT_MAX and zone->spanned_pages is 1? So at least the 
max/min should be swapped?
Also the zone_end_pfn(zone) on the second line already sees the changes 
to zone->zone_start_pfn in the first line, so it's kind of a mess. You 
should probably cache zone_end_pfn() to a temporary variable before 
changing zone_start_pfn.

> +	}

I'm guessing the initial values come from this part in patch 2/6:

> @@ -5723,6 +5738,8 @@ static void __meminit calculate_node_totalpages(struct pglist_data *pgdat,
>                                                 unsigned long *zholes_size)
>  {
>         unsigned long realtotalpages = 0, totalpages = 0;
> +       unsigned long zone_cma_start_pfn = UINT_MAX;
> +       unsigned long zone_cma_end_pfn = 0;
>         enum zone_type i;
>
>         for (i = 0; i < MAX_NR_ZONES; i++) {
> @@ -5730,6 +5747,13 @@ static void __meminit calculate_node_totalpages(struct pglist_data *pgdat,
>                 unsigned long zone_start_pfn, zone_end_pfn;
>                 unsigned long size, real_size;
>
> +               if (is_zone_cma_idx(i)) {
> +                       zone->zone_start_pfn = zone_cma_start_pfn;
> +                       size = zone_cma_end_pfn - zone_cma_start_pfn;
> +                       real_size = 0;
> +                       goto init_zone;
> +               }