Re: [PATCH] hibernate / memory hotplug: always use for_each_populated_zone()

["Rafael J. Wysocki" <rjw@sisk.pl>]

On Monday 20 July 2009, Gerald Schaefer wrote:
> From: Gerald Schaefer <gerald.schaefer@de.ibm.com>
> 
> Use for_each_populated_zone() instead of for_each_zone() in hibernation
> code. This fixes a bug on s390, where we allow both config options
> HIBERNATION and MEMORY_HOTPLUG, so that we also have a ZONE_MOVABLE
> here. We only allow hibernation if no memory hotplug operation was
> performed, so in fact both features can only be used exclusively, but
> this way we don't need 2 differently configured (distribution) kernels.
> 
> If we have an unpopulated ZONE_MOVABLE, we allow hibernation but run
> into a BUG_ON() in memory_bm_test/set/clear_bit() because hibernation
> code iterates through all zones, not only the populated zones, in
> several places. For example, swsusp_free() does for_each_zone() and
> then checks for pfn_valid(), which is true even if the zone is not
> populated, resulting in a BUG_ON() later because the pfn cannot be
> found in the memory bitmap.
> 
> Replacing all occurences of for_each_zone() in hibernation code with
> for_each_populated_zone() would fix this issue.

Thanks for the patch, I'm going to add it to my 2.6.32 queue.

Best,
Rafael


> Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
> ---
>  kernel/power/snapshot.c |   12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> Index: linux-2.6-work/kernel/power/snapshot.c
> ===================================================================
> --- linux-2.6-work.orig/kernel/power/snapshot.c
> +++ linux-2.6-work/kernel/power/snapshot.c
> @@ -853,7 +853,7 @@ static unsigned int count_highmem_pages(
>  	struct zone *zone;
>  	unsigned int n = 0;
>  
> -	for_each_zone(zone) {
> +	for_each_populated_zone(zone) {
>  		unsigned long pfn, max_zone_pfn;
>  
>  		if (!is_highmem(zone))
> @@ -916,7 +916,7 @@ static unsigned int count_data_pages(voi
>  	unsigned long pfn, max_zone_pfn;
>  	unsigned int n = 0;
>  
> -	for_each_zone(zone) {
> +	for_each_populated_zone(zone) {
>  		if (is_highmem(zone))
>  			continue;
>  
> @@ -1010,7 +1010,7 @@ copy_data_pages(struct memory_bitmap *co
>  	struct zone *zone;
>  	unsigned long pfn;
>  
> -	for_each_zone(zone) {
> +	for_each_populated_zone(zone) {
>  		unsigned long max_zone_pfn;
>  
>  		mark_free_pages(zone);
> @@ -1046,7 +1046,7 @@ void swsusp_free(void)
>  	struct zone *zone;
>  	unsigned long pfn, max_zone_pfn;
>  
> -	for_each_zone(zone) {
> +	for_each_populated_zone(zone) {
>  		max_zone_pfn = zone->zone_start_pfn + zone->spanned_pages;
>  		for (pfn = zone->zone_start_pfn; pfn < max_zone_pfn; pfn++)
>  			if (pfn_valid(pfn)) {
> @@ -1166,7 +1166,7 @@ static int enough_free_mem(unsigned int 
>  	struct zone *zone;
>  	unsigned int free = 0, meta = 0;
>  
> -	for_each_zone(zone) {
> +	for_each_populated_zone(zone) {
>  		meta += snapshot_additional_pages(zone);
>  		if (!is_highmem(zone))
>  			free += zone_page_state(zone, NR_FREE_PAGES);
> @@ -1474,7 +1474,7 @@ static int mark_unsafe_pages(struct memo
>  	unsigned long pfn, max_zone_pfn;
>  
>  	/* Clear page flags */
> -	for_each_zone(zone) {
> +	for_each_populated_zone(zone) {
>  		max_zone_pfn = zone->zone_start_pfn + zone->spanned_pages;
>  		for (pfn = zone->zone_start_pfn; pfn < max_zone_pfn; pfn++)
>  			if (pfn_valid(pfn))
> 
> 
>