[v12,01/11] mm: deferred_init_memmap improvements

deferred_init_memmap() is called when struct pages are initialized later
in boot by slave CPUs. This patch simplifies and optimizes this function,
and also fixes a couple issues (described below).

The main change is that now we are iterating through free memblock areas
instead of all configured memory. Thus, we do not have to check if the
struct page has already been initialized.

On Fri 13-10-17 13:32:04, Pavel Tatashin wrote:
> deferred_init_memmap() is called when struct pages are initialized later
> in boot by slave CPUs. This patch simplifies and optimizes this function,
> and also fixes a couple issues (described below).
> 
> The main change is that now we are iterating through free memblock areas
> instead of all configured memory. Thus, we do not have to check if the
> struct page has already been initialized.
> 
> =====
> In deferred_init_memmap() where all deferred struct pages are initialized
> we have a check like this:
> 
> if (page->flags) {
> 	VM_BUG_ON(page_zone(page) != zone);
> 	goto free_range;
> }
> 
> This way we are checking if the current deferred page has already been
> initialized. It works, because memory for struct pages has been zeroed, and
> the only way flags are not zero if it went through __init_single_page()
> before.  But, once we change the current behavior and won't zero the memory
> in memblock allocator, we cannot trust anything inside "struct page"es
> until they are initialized. This patch fixes this.
> 
> The deferred_init_memmap() is re-written to loop through only free memory
> ranges provided by memblock.
> 
> Note, this first issue is relevant only when the following change is
> merged:
> 
> =====
> This patch fixes another existing issue on systems that have holes in
> zones i.e CONFIG_HOLES_IN_ZONE is defined.
> 
> In for_each_mem_pfn_range() we have code like this:
> 
> if (!pfn_valid_within(pfn)
> 	goto free_range;
> 
> Note: 'page' is not set to NULL and is not incremented but 'pfn' advances.
> Thus means if deferred struct pages are enabled on systems with these kind
> of holes, linux would get memory corruptions. I have fixed this issue by
> defining a new macro that performs all the necessary operations when we
> free the current set of pages.

This really begs to have two patches... I will not insist though. I also
suspect the code can be further simplified but again this is nothing to
block this to go.
 
> Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com>
> Reviewed-by: Steven Sistare <steven.sistare@oracle.com>
> Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com>
> Reviewed-by: Bob Picco <bob.picco@oracle.com>

I do not see any obvious issues in the patch

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
>  mm/page_alloc.c | 168 ++++++++++++++++++++++++++++----------------------------
>  1 file changed, 85 insertions(+), 83 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 77e4d3c5c57b..cdbd14829fd3 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1410,14 +1410,17 @@ void clear_zone_contiguous(struct zone *zone)
>  }
>  
>  #ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
> -static void __init deferred_free_range(struct page *page,
> -					unsigned long pfn, int nr_pages)
> +static void __init deferred_free_range(unsigned long pfn,
> +				       unsigned long nr_pages)
>  {
> -	int i;
> +	struct page *page;
> +	unsigned long i;
>  
> -	if (!page)
> +	if (!nr_pages)
>  		return;
>  
> +	page = pfn_to_page(pfn);
> +
>  	/* Free a large naturally-aligned chunk if possible */
>  	if (nr_pages == pageblock_nr_pages &&
>  	    (pfn & (pageblock_nr_pages - 1)) == 0) {
> @@ -1443,19 +1446,89 @@ static inline void __init pgdat_init_report_one_done(void)
>  		complete(&pgdat_init_all_done_comp);
>  }
>  
> +/*
> + * Helper for deferred_init_range, free the given range, reset the counters, and
> + * return number of pages freed.
> + */
> +static inline unsigned long __def_free(unsigned long *nr_free,
> +				       unsigned long *free_base_pfn,
> +				       struct page **page)
> +{
> +	unsigned long nr = *nr_free;
> +
> +	deferred_free_range(*free_base_pfn, nr);
> +	*free_base_pfn = 0;
> +	*nr_free = 0;
> +	*page = NULL;
> +
> +	return nr;
> +}
> +
> +static unsigned long deferred_init_range(int nid, int zid, unsigned long pfn,
> +					 unsigned long end_pfn)
> +{
> +	struct mminit_pfnnid_cache nid_init_state = { };
> +	unsigned long nr_pgmask = pageblock_nr_pages - 1;
> +	unsigned long free_base_pfn = 0;
> +	unsigned long nr_pages = 0;
> +	unsigned long nr_free = 0;
> +	struct page *page = NULL;
> +
> +	for (; pfn < end_pfn; pfn++) {
> +		/*
> +		 * First we check if pfn is valid on architectures where it is
> +		 * possible to have holes within pageblock_nr_pages. On systems
> +		 * where it is not possible, this function is optimized out.
> +		 *
> +		 * Then, we check if a current large page is valid by only
> +		 * checking the validity of the head pfn.
> +		 *
> +		 * meminit_pfn_in_nid is checked on systems where pfns can
> +		 * interleave within a node: a pfn is between start and end
> +		 * of a node, but does not belong to this memory node.
> +		 *
> +		 * Finally, we minimize pfn page lookups and scheduler checks by
> +		 * performing it only once every pageblock_nr_pages.
> +		 */
> +		if (!pfn_valid_within(pfn)) {
> +			nr_pages += __def_free(&nr_free, &free_base_pfn, &page);
> +		} else if (!(pfn & nr_pgmask) && !pfn_valid(pfn)) {
> +			nr_pages += __def_free(&nr_free, &free_base_pfn, &page);
> +		} else if (!meminit_pfn_in_nid(pfn, nid, &nid_init_state)) {
> +			nr_pages += __def_free(&nr_free, &free_base_pfn, &page);
> +		} else if (page && (pfn & nr_pgmask)) {
> +			page++;
> +			__init_single_page(page, pfn, zid, nid);
> +			nr_free++;
> +		} else {
> +			nr_pages += __def_free(&nr_free, &free_base_pfn, &page);
> +			page = pfn_to_page(pfn);
> +			__init_single_page(page, pfn, zid, nid);
> +			free_base_pfn = pfn;
> +			nr_free = 1;
> +			cond_resched();
> +		}
> +	}
> +	/* Free the last block of pages to allocator */
> +	nr_pages += __def_free(&nr_free, &free_base_pfn, &page);
> +
> +	return nr_pages;
> +}
> +
>  /* Initialise remaining memory on a node */
>  static int __init deferred_init_memmap(void *data)
>  {
>  	pg_data_t *pgdat = data;
>  	int nid = pgdat->node_id;
> -	struct mminit_pfnnid_cache nid_init_state = { };
>  	unsigned long start = jiffies;
>  	unsigned long nr_pages = 0;
> -	unsigned long walk_start, walk_end;
> -	int i, zid;
> +	unsigned long spfn, epfn;
> +	phys_addr_t spa, epa;
> +	int zid;
>  	struct zone *zone;
>  	unsigned long first_init_pfn = pgdat->first_deferred_pfn;
>  	const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
> +	u64 i;
>  
>  	if (first_init_pfn == ULONG_MAX) {
>  		pgdat_init_report_one_done();
> @@ -1477,83 +1550,12 @@ static int __init deferred_init_memmap(void *data)
>  		if (first_init_pfn < zone_end_pfn(zone))
>  			break;
>  	}
> +	first_init_pfn = max(zone->zone_start_pfn, first_init_pfn);
>  
> -	for_each_mem_pfn_range(i, nid, &walk_start, &walk_end, NULL) {
> -		unsigned long pfn, end_pfn;
> -		struct page *page = NULL;
> -		struct page *free_base_page = NULL;
> -		unsigned long free_base_pfn = 0;
> -		int nr_to_free = 0;
> -
> -		end_pfn = min(walk_end, zone_end_pfn(zone));
> -		pfn = first_init_pfn;
> -		if (pfn < walk_start)
> -			pfn = walk_start;
> -		if (pfn < zone->zone_start_pfn)
> -			pfn = zone->zone_start_pfn;
> -
> -		for (; pfn < end_pfn; pfn++) {
> -			if (!pfn_valid_within(pfn))
> -				goto free_range;
> -
> -			/*
> -			 * Ensure pfn_valid is checked every
> -			 * pageblock_nr_pages for memory holes
> -			 */
> -			if ((pfn & (pageblock_nr_pages - 1)) == 0) {
> -				if (!pfn_valid(pfn)) {
> -					page = NULL;
> -					goto free_range;
> -				}
> -			}
> -
> -			if (!meminit_pfn_in_nid(pfn, nid, &nid_init_state)) {
> -				page = NULL;
> -				goto free_range;
> -			}
> -
> -			/* Minimise pfn page lookups and scheduler checks */
> -			if (page && (pfn & (pageblock_nr_pages - 1)) != 0) {
> -				page++;
> -			} else {
> -				nr_pages += nr_to_free;
> -				deferred_free_range(free_base_page,
> -						free_base_pfn, nr_to_free);
> -				free_base_page = NULL;
> -				free_base_pfn = nr_to_free = 0;
> -
> -				page = pfn_to_page(pfn);
> -				cond_resched();
> -			}
> -
> -			if (page->flags) {
> -				VM_BUG_ON(page_zone(page) != zone);
> -				goto free_range;
> -			}
> -
> -			__init_single_page(page, pfn, zid, nid);
> -			if (!free_base_page) {
> -				free_base_page = page;
> -				free_base_pfn = pfn;
> -				nr_to_free = 0;
> -			}
> -			nr_to_free++;
> -
> -			/* Where possible, batch up pages for a single free */
> -			continue;
> -free_range:
> -			/* Free the current block of pages to allocator */
> -			nr_pages += nr_to_free;
> -			deferred_free_range(free_base_page, free_base_pfn,
> -								nr_to_free);
> -			free_base_page = NULL;
> -			free_base_pfn = nr_to_free = 0;
> -		}
> -		/* Free the last block of pages to allocator */
> -		nr_pages += nr_to_free;
> -		deferred_free_range(free_base_page, free_base_pfn, nr_to_free);
> -
> -		first_init_pfn = max(end_pfn, first_init_pfn);
> +	for_each_free_mem_range(i, nid, MEMBLOCK_NONE, &spa, &epa, NULL) {
> +		spfn = max_t(unsigned long, first_init_pfn, PFN_UP(spa));
> +		epfn = min_t(unsigned long, zone_end_pfn(zone), PFN_DOWN(epa));
> +		nr_pages += deferred_init_range(nid, zid, spfn, epfn);
>  	}
>  
>  	/* Sanity check that the next zone really is unpopulated */
> -- 
> 2.14.2

> This really begs to have two patches... I will not insist though. I also
> suspect the code can be further simplified but again this is nothing to
> block this to go.

Perhaps "page" can be avoided in deferred_init_range(), as pfn is 
converted to page in deferred_free_range, but I have not studied it.

>   
>> Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com>
>> Reviewed-by: Steven Sistare <steven.sistare@oracle.com>
>> Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com>
>> Reviewed-by: Bob Picco <bob.picco@oracle.com>
> 
> I do not see any obvious issues in the patch
> 
> Acked-by: Michal Hocko <mhocko@suse.com>

Thank you very much!

Pavel

> 
>> ---
>>   mm/page_alloc.c | 168 ++++++++++++++++++++++++++++----------------------------
>>   1 file changed, 85 insertions(+), 83 deletions(-)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 77e4d3c5c57b..cdbd14829fd3 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -1410,14 +1410,17 @@ void clear_zone_contiguous(struct zone *zone)
>>   }
>>   
>>   #ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
>> -static void __init deferred_free_range(struct page *page,
>> -					unsigned long pfn, int nr_pages)
>> +static void __init deferred_free_range(unsigned long pfn,
>> +				       unsigned long nr_pages)
>>   {
>> -	int i;
>> +	struct page *page;
>> +	unsigned long i;
>>   
>> -	if (!page)
>> +	if (!nr_pages)
>>   		return;
>>   
>> +	page = pfn_to_page(pfn);
>> +
>>   	/* Free a large naturally-aligned chunk if possible */
>>   	if (nr_pages == pageblock_nr_pages &&
>>   	    (pfn & (pageblock_nr_pages - 1)) == 0) {
>> @@ -1443,19 +1446,89 @@ static inline void __init pgdat_init_report_one_done(void)
>>   		complete(&pgdat_init_all_done_comp);
>>   }
>>   
>> +/*
>> + * Helper for deferred_init_range, free the given range, reset the counters, and
>> + * return number of pages freed.
>> + */
>> +static inline unsigned long __def_free(unsigned long *nr_free,
>> +				       unsigned long *free_base_pfn,
>> +				       struct page **page)
>> +{
>> +	unsigned long nr = *nr_free;
>> +
>> +	deferred_free_range(*free_base_pfn, nr);
>> +	*free_base_pfn = 0;
>> +	*nr_free = 0;
>> +	*page = NULL;
>> +
>> +	return nr;
>> +}
>> +
>> +static unsigned long deferred_init_range(int nid, int zid, unsigned long pfn,
>> +					 unsigned long end_pfn)
>> +{
>> +	struct mminit_pfnnid_cache nid_init_state = { };
>> +	unsigned long nr_pgmask = pageblock_nr_pages - 1;
>> +	unsigned long free_base_pfn = 0;
>> +	unsigned long nr_pages = 0;
>> +	unsigned long nr_free = 0;
>> +	struct page *page = NULL;
>> +
>> +	for (; pfn < end_pfn; pfn++) {
>> +		/*
>> +		 * First we check if pfn is valid on architectures where it is
>> +		 * possible to have holes within pageblock_nr_pages. On systems
>> +		 * where it is not possible, this function is optimized out.
>> +		 *
>> +		 * Then, we check if a current large page is valid by only
>> +		 * checking the validity of the head pfn.
>> +		 *
>> +		 * meminit_pfn_in_nid is checked on systems where pfns can
>> +		 * interleave within a node: a pfn is between start and end
>> +		 * of a node, but does not belong to this memory node.
>> +		 *
>> +		 * Finally, we minimize pfn page lookups and scheduler checks by
>> +		 * performing it only once every pageblock_nr_pages.
>> +		 */
>> +		if (!pfn_valid_within(pfn)) {
>> +			nr_pages += __def_free(&nr_free, &free_base_pfn, &page);
>> +		} else if (!(pfn & nr_pgmask) && !pfn_valid(pfn)) {
>> +			nr_pages += __def_free(&nr_free, &free_base_pfn, &page);
>> +		} else if (!meminit_pfn_in_nid(pfn, nid, &nid_init_state)) {
>> +			nr_pages += __def_free(&nr_free, &free_base_pfn, &page);
>> +		} else if (page && (pfn & nr_pgmask)) {
>> +			page++;
>> +			__init_single_page(page, pfn, zid, nid);
>> +			nr_free++;
>> +		} else {
>> +			nr_pages += __def_free(&nr_free, &free_base_pfn, &page);
>> +			page = pfn_to_page(pfn);
>> +			__init_single_page(page, pfn, zid, nid);
>> +			free_base_pfn = pfn;
>> +			nr_free = 1;
>> +			cond_resched();
>> +		}
>> +	}
>> +	/* Free the last block of pages to allocator */
>> +	nr_pages += __def_free(&nr_free, &free_base_pfn, &page);
>> +
>> +	return nr_pages;
>> +}
>> +
>>   /* Initialise remaining memory on a node */
>>   static int __init deferred_init_memmap(void *data)
>>   {
>>   	pg_data_t *pgdat = data;
>>   	int nid = pgdat->node_id;
>> -	struct mminit_pfnnid_cache nid_init_state = { };
>>   	unsigned long start = jiffies;
>>   	unsigned long nr_pages = 0;
>> -	unsigned long walk_start, walk_end;
>> -	int i, zid;
>> +	unsigned long spfn, epfn;
>> +	phys_addr_t spa, epa;
>> +	int zid;
>>   	struct zone *zone;
>>   	unsigned long first_init_pfn = pgdat->first_deferred_pfn;
>>   	const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
>> +	u64 i;
>>   
>>   	if (first_init_pfn == ULONG_MAX) {
>>   		pgdat_init_report_one_done();
>> @@ -1477,83 +1550,12 @@ static int __init deferred_init_memmap(void *data)
>>   		if (first_init_pfn < zone_end_pfn(zone))
>>   			break;
>>   	}
>> +	first_init_pfn = max(zone->zone_start_pfn, first_init_pfn);
>>   
>> -	for_each_mem_pfn_range(i, nid, &walk_start, &walk_end, NULL) {
>> -		unsigned long pfn, end_pfn;
>> -		struct page *page = NULL;
>> -		struct page *free_base_page = NULL;
>> -		unsigned long free_base_pfn = 0;
>> -		int nr_to_free = 0;
>> -
>> -		end_pfn = min(walk_end, zone_end_pfn(zone));
>> -		pfn = first_init_pfn;
>> -		if (pfn < walk_start)
>> -			pfn = walk_start;
>> -		if (pfn < zone->zone_start_pfn)
>> -			pfn = zone->zone_start_pfn;
>> -
>> -		for (; pfn < end_pfn; pfn++) {
>> -			if (!pfn_valid_within(pfn))
>> -				goto free_range;
>> -
>> -			/*
>> -			 * Ensure pfn_valid is checked every
>> -			 * pageblock_nr_pages for memory holes
>> -			 */
>> -			if ((pfn & (pageblock_nr_pages - 1)) == 0) {
>> -				if (!pfn_valid(pfn)) {
>> -					page = NULL;
>> -					goto free_range;
>> -				}
>> -			}
>> -
>> -			if (!meminit_pfn_in_nid(pfn, nid, &nid_init_state)) {
>> -				page = NULL;
>> -				goto free_range;
>> -			}
>> -
>> -			/* Minimise pfn page lookups and scheduler checks */
>> -			if (page && (pfn & (pageblock_nr_pages - 1)) != 0) {
>> -				page++;
>> -			} else {
>> -				nr_pages += nr_to_free;
>> -				deferred_free_range(free_base_page,
>> -						free_base_pfn, nr_to_free);
>> -				free_base_page = NULL;
>> -				free_base_pfn = nr_to_free = 0;
>> -
>> -				page = pfn_to_page(pfn);
>> -				cond_resched();
>> -			}
>> -
>> -			if (page->flags) {
>> -				VM_BUG_ON(page_zone(page) != zone);
>> -				goto free_range;
>> -			}
>> -
>> -			__init_single_page(page, pfn, zid, nid);
>> -			if (!free_base_page) {
>> -				free_base_page = page;
>> -				free_base_pfn = pfn;
>> -				nr_to_free = 0;
>> -			}
>> -			nr_to_free++;
>> -
>> -			/* Where possible, batch up pages for a single free */
>> -			continue;
>> -free_range:
>> -			/* Free the current block of pages to allocator */
>> -			nr_pages += nr_to_free;
>> -			deferred_free_range(free_base_page, free_base_pfn,
>> -								nr_to_free);
>> -			free_base_page = NULL;
>> -			free_base_pfn = nr_to_free = 0;
>> -		}
>> -		/* Free the last block of pages to allocator */
>> -		nr_pages += nr_to_free;
>> -		deferred_free_range(free_base_page, free_base_pfn, nr_to_free);
>> -
>> -		first_init_pfn = max(end_pfn, first_init_pfn);
>> +	for_each_free_mem_range(i, nid, MEMBLOCK_NONE, &spa, &epa, NULL) {
>> +		spfn = max_t(unsigned long, first_init_pfn, PFN_UP(spa));
>> +		epfn = min_t(unsigned long, zone_end_pfn(zone), PFN_DOWN(epa));
>> +		nr_pages += deferred_init_range(nid, zid, spfn, epfn);
>>   	}
>>   
>>   	/* Sanity check that the next zone really is unpopulated */
>> -- 
>> 2.14.2
> 
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