Re: [PATCH] mm/page_alloc: Make alloc_gigantic_page() available for general use

[Michal Hocko]

On Wed 16-10-19 13:04:53, Anshuman Khandual wrote:
> HugeTLB helper alloc_gigantic_page() implements fairly generic allocation
> method where it scans over various zones looking for a large contiguous pfn
> range before trying to allocate it with alloc_contig_range(). Other than
> deriving the requested order from 'struct hstate', there is nothing HugeTLB
> specific in there. This can be made available for general use to allocate
> contiguous memory which could not have been allocated through the buddy
> allocator.
> 
> alloc_gigantic_page() has been split carving out actual allocation method
> which is then made available via new alloc_contig_pages() helper wrapped
> under CONFIG_CONTIG_ALLOC. All references to 'gigantic' have been replaced
> with more generic term 'contig'. Allocated pages here should be freed with
> free_contig_range() or by calling __free_page() on each allocated page.

Do we want to export this to modules? Apart from mostly styling issues
pointed by David this looks fine.

I do agree that a general allocator api belongs to page_alloc.c rather
than force people to invent their own and broken instances.
 
> Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> Cc: Oscar Salvador <osalvador@xxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
> Cc: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Cc: Pavel Tatashin <pavel.tatashin@xxxxxxxxxxxxx>
> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Cc: David Hildenbrand <david@xxxxxxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>

After other issues mentioned by David get resolved you can add
Acked-by: Michal Hocko <mhocko@xxxxxxxx>

> ---
> This is based on https://patchwork.kernel.org/patch/11190213/
> 
> Changes from [V5,1/2] mm/hugetlb: Make alloc_gigantic_page()...
> 
> - alloc_contig_page() takes nr_pages instead of order per Michal
> - s/gigantic/contig on all related functions
> 
>  include/linux/gfp.h |  2 +
>  mm/hugetlb.c        | 77 +----------------------------------
>  mm/page_alloc.c     | 97 +++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 101 insertions(+), 75 deletions(-)
> 
> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> index fb07b503dc45..1a11d4857027 100644
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -589,6 +589,8 @@ static inline bool pm_suspended_storage(void)
>  /* The below functions must be run on a range from a single zone. */
>  extern int alloc_contig_range(unsigned long start, unsigned long end,
>  			      unsigned migratetype, gfp_t gfp_mask);
> +extern struct page *alloc_contig_pages(unsigned long nr_pages, gfp_t gfp_mask,
> +				       int nid, nodemask_t *nodemask);
>  #endif
>  void free_contig_range(unsigned long pfn, unsigned int nr_pages);
>  
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 985ee15eb04b..a5c2c880af27 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1023,85 +1023,12 @@ static void free_gigantic_page(struct page *page, unsigned int order)
>  }
>  
>  #ifdef CONFIG_CONTIG_ALLOC
> -static int __alloc_gigantic_page(unsigned long start_pfn,
> -				unsigned long nr_pages, gfp_t gfp_mask)
> -{
> -	unsigned long end_pfn = start_pfn + nr_pages;
> -	return alloc_contig_range(start_pfn, end_pfn, MIGRATE_MOVABLE,
> -				  gfp_mask);
> -}
> -
> -static bool pfn_range_valid_gigantic(struct zone *z,
> -			unsigned long start_pfn, unsigned long nr_pages)
> -{
> -	unsigned long i, end_pfn = start_pfn + nr_pages;
> -	struct page *page;
> -
> -	for (i = start_pfn; i < end_pfn; i++) {
> -		page = pfn_to_online_page(i);
> -		if (!page)
> -			return false;
> -
> -		if (page_zone(page) != z)
> -			return false;
> -
> -		if (PageReserved(page))
> -			return false;
> -
> -		if (page_count(page) > 0)
> -			return false;
> -
> -		if (PageHuge(page))
> -			return false;
> -	}
> -
> -	return true;
> -}
> -
> -static bool zone_spans_last_pfn(const struct zone *zone,
> -			unsigned long start_pfn, unsigned long nr_pages)
> -{
> -	unsigned long last_pfn = start_pfn + nr_pages - 1;
> -	return zone_spans_pfn(zone, last_pfn);
> -}
> -
>  static struct page *alloc_gigantic_page(struct hstate *h, gfp_t gfp_mask,
>  		int nid, nodemask_t *nodemask)
>  {
> -	unsigned int order = huge_page_order(h);
> -	unsigned long nr_pages = 1 << order;
> -	unsigned long ret, pfn, flags;
> -	struct zonelist *zonelist;
> -	struct zone *zone;
> -	struct zoneref *z;
> -
> -	zonelist = node_zonelist(nid, gfp_mask);
> -	for_each_zone_zonelist_nodemask(zone, z, zonelist, gfp_zone(gfp_mask), nodemask) {
> -		spin_lock_irqsave(&zone->lock, flags);
> +	unsigned long nr_pages = 1UL << huge_page_order(h);
>  
> -		pfn = ALIGN(zone->zone_start_pfn, nr_pages);
> -		while (zone_spans_last_pfn(zone, pfn, nr_pages)) {
> -			if (pfn_range_valid_gigantic(zone, pfn, nr_pages)) {
> -				/*
> -				 * We release the zone lock here because
> -				 * alloc_contig_range() will also lock the zone
> -				 * at some point. If there's an allocation
> -				 * spinning on this lock, it may win the race
> -				 * and cause alloc_contig_range() to fail...
> -				 */
> -				spin_unlock_irqrestore(&zone->lock, flags);
> -				ret = __alloc_gigantic_page(pfn, nr_pages, gfp_mask);
> -				if (!ret)
> -					return pfn_to_page(pfn);
> -				spin_lock_irqsave(&zone->lock, flags);
> -			}
> -			pfn += nr_pages;
> -		}
> -
> -		spin_unlock_irqrestore(&zone->lock, flags);
> -	}
> -
> -	return NULL;
> +	return alloc_contig_pages(nr_pages, gfp_mask, nid, nodemask);
>  }
>  
>  static void prep_new_huge_page(struct hstate *h, struct page *page, int nid);
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index cd1dd0712624..1e084d6acf2f 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -8499,6 +8499,103 @@ int alloc_contig_range(unsigned long start, unsigned long end,
>  				pfn_max_align_up(end), migratetype);
>  	return ret;
>  }
> +
> +static int __alloc_contig_pages(unsigned long start_pfn,
> +				unsigned long nr_pages, gfp_t gfp_mask)
> +{
> +	unsigned long end_pfn = start_pfn + nr_pages;
> +
> +	return alloc_contig_range(start_pfn, end_pfn, MIGRATE_MOVABLE,
> +				  gfp_mask);
> +}
> +
> +static bool pfn_range_valid_contig(struct zone *z, unsigned long start_pfn,
> +				   unsigned long nr_pages)
> +{
> +	unsigned long i, end_pfn = start_pfn + nr_pages;
> +	struct page *page;
> +
> +	for (i = start_pfn; i < end_pfn; i++) {
> +		page = pfn_to_online_page(i);
> +		if (!page)
> +			return false;
> +
> +		if (page_zone(page) != z)
> +			return false;
> +
> +		if (PageReserved(page))
> +			return false;
> +
> +		if (page_count(page) > 0)
> +			return false;
> +
> +		if (PageHuge(page))
> +			return false;
> +	}
> +	return true;
> +}
> +
> +static bool zone_spans_last_pfn(const struct zone *zone,
> +				unsigned long start_pfn, unsigned long nr_pages)
> +{
> +	unsigned long last_pfn = start_pfn + nr_pages - 1;
> +
> +	return zone_spans_pfn(zone, last_pfn);
> +}
> +
> +/**
> + * alloc_contig_pages() -- tries to find and allocate contiguous range of pages
> + * @nr_pages:	Number of contiguous pages to allocate
> + * @gfp_mask:	GFP mask to limit search and used during compaction
> + * @nid:	Target node
> + * @nodemask:	Mask for other possible nodes
> + *
> + * This routine is an wrapper around alloc_contig_range(). It scans over zones
> + * on an applicable zonelist to find a contiguous pfn range which can then be
> + * tried for allocation with alloc_contig_range(). This routine is intended
> + * for allocation requests which can not be fulfilled with buddy allocator.
> + *
> + * Allocated pages can be freed with free_contig_range() or by manually calling
> + * __free_page() on each allocated page.
> + *
> + * Return: pointer to 'order' pages on success, or NULL if not successful.
> + */
> +struct page *alloc_contig_pages(unsigned long nr_pages, gfp_t gfp_mask,
> +				int nid, nodemask_t *nodemask)
> +{
> +	unsigned long ret, pfn, flags;
> +	struct zonelist *zonelist;
> +	struct zone *zone;
> +	struct zoneref *z;
> +
> +	zonelist = node_zonelist(nid, gfp_mask);
> +	for_each_zone_zonelist_nodemask(zone, z, zonelist,
> +					gfp_zone(gfp_mask), nodemask) {
> +		spin_lock_irqsave(&zone->lock, flags);
> +
> +		pfn = ALIGN(zone->zone_start_pfn, nr_pages);
> +		while (zone_spans_last_pfn(zone, pfn, nr_pages)) {
> +			if (pfn_range_valid_contig(zone, pfn, nr_pages)) {
> +				/*
> +				 * We release the zone lock here because
> +				 * alloc_contig_range() will also lock the zone
> +				 * at some point. If there's an allocation
> +				 * spinning on this lock, it may win the race
> +				 * and cause alloc_contig_range() to fail...
> +				 */
> +				spin_unlock_irqrestore(&zone->lock, flags);
> +				ret = __alloc_contig_pages(pfn, nr_pages,
> +							gfp_mask);
> +				if (!ret)
> +					return pfn_to_page(pfn);
> +				spin_lock_irqsave(&zone->lock, flags);
> +			}
> +			pfn += nr_pages;
> +		}
> +		spin_unlock_irqrestore(&zone->lock, flags);
> +	}
> +	return NULL;
> +}
>  #endif /* CONFIG_CONTIG_ALLOC */
>  
>  void free_contig_range(unsigned long pfn, unsigned int nr_pages)
> -- 
> 2.20.1

-- 
Michal Hocko
SUSE Labs