linux-kernel - Re: [PATCH] mm: use managed_zone() for more exact check in zone iteration

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Date:   Fri, 16 Nov 2018 11:24:05 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Wei Yang <richard.weiyang@...il.com>
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        "Rafael J. Wysocki" <rjw@...ysocki.net>
Subject: Re: [PATCH] mm: use managed_zone() for more exact check in zone
 iteration

On Thu 15-11-18 07:50:40, Wei Yang wrote:
[...]
> @@ -1193,8 +1196,8 @@ static unsigned int count_free_highmem_pages(void)
>  	struct zone *zone;
>  	unsigned int cnt = 0;
>  
> -	for_each_populated_zone(zone)
> -		if (is_highmem(zone))
> +	for_each_zone(zone)
> +		if (populated_zone(zone) && is_highmem(zone))
>  			cnt += zone_page_state(zone, NR_FREE_PAGES);

this should be for_each_managed_zone because we only care about highmem
zones which have pages in the allocator (NR_FREE_PAGES).

>  
>  	return cnt;
> @@ -1239,10 +1242,10 @@ static unsigned int count_highmem_pages(void)
>  	struct zone *zone;
>  	unsigned int n = 0;
>  
> -	for_each_populated_zone(zone) {
> +	for_each_zone(zone) {
>  		unsigned long pfn, max_zone_pfn;
>  
> -		if (!is_highmem(zone))
> +		if (!populated_zone(zone) || !is_highmem(zone))
>  			continue;
>  
>  		mark_free_pages(zone);

I am not familiar with this code much but I strongly suspect that we do
want for_each_managed_zone here because saveable_highmem_page skips over
all reserved pages which rules out the bootmem. But this should be
double checked with Rafael (Cc-ed).

Rafael, does this loop care about pages which are not managed by the
page allocator?

> @@ -1305,8 +1308,8 @@ static unsigned int count_data_pages(void)
>  	unsigned long pfn, max_zone_pfn;
>  	unsigned int n = 0;
>  
> -	for_each_populated_zone(zone) {
> -		if (is_highmem(zone))
> +	for_each_zone(zone) {
> +		if (!populated_zone(zone) || is_highmem(zone))
>  			continue;
>  
>  		mark_free_pages(zone);
> @@ -1399,9 +1402,12 @@ static void copy_data_pages(struct memory_bitmap *copy_bm,
>  	struct zone *zone;
>  	unsigned long pfn;
>  
> -	for_each_populated_zone(zone) {
> +	for_each_zone(zone) {
>  		unsigned long max_zone_pfn;
>  
> +		if (!populated_zone(zone))
> +			continue;
> +
>  		mark_free_pages(zone);
>  		max_zone_pfn = zone_end_pfn(zone);
>  		for (pfn = zone->zone_start_pfn; pfn < max_zone_pfn; pfn++)
> @@ -1717,7 +1723,10 @@ int hibernate_preallocate_memory(void)
>  	saveable += save_highmem;
>  	highmem = save_highmem;
>  	size = 0;
> -	for_each_populated_zone(zone) {
> +	for_each_zone(zone) {
> +		if (!populated_zone(zone))
> +			continue;
> +
>  		size += snapshot_additional_pages(zone);
>  		if (is_highmem(zone))
>  			highmem += zone_page_state(zone, NR_FREE_PAGES);

ditto for the above.


> @@ -1863,8 +1872,8 @@ static int enough_free_mem(unsigned int nr_pages, unsigned int nr_highmem)
>  	struct zone *zone;
>  	unsigned int free = alloc_normal;
>  
> -	for_each_populated_zone(zone)
> -		if (!is_highmem(zone))
> +	for_each_zone(zone)
> +		if (populated_zone(zone) && !is_highmem(zone))
>  			free += zone_page_state(zone, NR_FREE_PAGES);
>  
>  	nr_pages += count_pages_for_highmem(nr_highmem);

This one should be for_each_managed_zone (NR_FREE_PAGES)

The rest looks good to me.
-- 
Michal Hocko
SUSE Labs