Re: [PATCH] mm/vmalloc: introduce alloc_pages_bulk_array_mempolicy to accelerate memory allocation

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 14 Oct 2021 17:29:52 +0800 Chen Wandun <chenwandun@huawei.com> wrote:

> It will cause significant performance regressions in some situations
> as Andrew mentioned in [1]. The main situation is vmalloc, vmalloc
> will allocate pages with NUMA_NO_NODE by default, that will result
> in alloc page one by one;
> 
> In order to solve this, __alloc_pages_bulk and mempolicy should be
> considered at the same time.
> 
> 1) If node is specified in memory allocation request, it will alloc
> all pages by __alloc_pages_bulk.
> 
> 2) If interleaving allocate memory, it will cauculate how many pages
> should be allocated in each node, and use __alloc_pages_bulk to alloc
> pages in each node.
> 
> [1]: https://lore.kernel.org/lkml/CALvZod4G3SzP3kWxQYn0fj+VgG-G3yWXz=gz17+3N57ru1iajw@mail.gmail.com/t/#m750c8e3231206134293b089feaa090590afa0f60
> 
> ...
>
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -531,6 +531,10 @@ unsigned long __alloc_pages_bulk(gfp_t gfp, int preferred_nid,
>  				struct list_head *page_list,
>  				struct page **page_array);
>  
> +unsigned long alloc_pages_bulk_array_mempolicy(gfp_t gfp,
> +				unsigned long nr_pages,
> +				struct page **page_array);
> +
>  /* Bulk allocate order-0 pages */
>  static inline unsigned long
>  alloc_pages_bulk_list(gfp_t gfp, unsigned long nr_pages, struct list_head *list)
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 9f8cd1457829..f456c5eb8d10 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -2196,6 +2196,82 @@ struct page *alloc_pages(gfp_t gfp, unsigned order)
>  }
>  EXPORT_SYMBOL(alloc_pages);
>  
> +unsigned long alloc_pages_bulk_array_interleave(gfp_t gfp,
> +		struct mempolicy *pol, unsigned long nr_pages,
> +		struct page **page_array)

I'll make this static.

> +{
> +	int nodes;
> +	unsigned long nr_pages_per_node;
> +	int delta;
> +	int i;
> +	unsigned long nr_allocated;
> +	unsigned long total_allocated = 0;
> +
> +	nodes = nodes_weight(pol->nodes);
> +	nr_pages_per_node = nr_pages / nodes;
> +	delta = nr_pages - nodes * nr_pages_per_node;
> +
> +	for (i = 0; i < nodes; i++) {
> +		if (delta) {
> +			nr_allocated = __alloc_pages_bulk(gfp,
> +					interleave_nodes(pol), NULL,
> +					nr_pages_per_node + 1, NULL,
> +					page_array);
> +			delta--;
> +		} else {
> +			nr_allocated = __alloc_pages_bulk(gfp,
> +					interleave_nodes(pol), NULL,
> +					nr_pages_per_node, NULL, page_array);
> +		}
> +
> +		page_array += nr_allocated;
> +		total_allocated += nr_allocated;
> +	}
> +
> +	return total_allocated;
> +}
> +
> +unsigned long alloc_pages_bulk_array_preferred_many(gfp_t gfp, int nid,
> +		struct mempolicy *pol, unsigned long nr_pages,
> +		struct page **page_array)

And this.

> +{
> +	gfp_t preferred_gfp;
> +	unsigned long nr_allocated = 0;
> +
> +	preferred_gfp = gfp | __GFP_NOWARN;
> +	preferred_gfp &= ~(__GFP_DIRECT_RECLAIM | __GFP_NOFAIL);
> +
> +	nr_allocated  = __alloc_pages_bulk(preferred_gfp, nid, &pol->nodes,
> +					   nr_pages, NULL, page_array);
> +
> +	if (nr_allocated < nr_pages)
> +		nr_allocated += __alloc_pages_bulk(gfp, numa_node_id(), NULL,
> +				nr_pages - nr_allocated, NULL,
> +				page_array + nr_allocated);
> +	return nr_allocated;
> +}
> +
> +unsigned long alloc_pages_bulk_array_mempolicy(gfp_t gfp,
> +		unsigned long nr_pages, struct page **page_array)
> +{
> +	struct mempolicy *pol = &default_policy;
> +
> +	if (!in_interrupt() && !(gfp & __GFP_THISNODE))
> +		pol = get_task_policy(current);
> +
> +	if (pol->mode == MPOL_INTERLEAVE)
> +		return alloc_pages_bulk_array_interleave(gfp, pol,
> +							 nr_pages, page_array);
> +
> +	if (pol->mode == MPOL_PREFERRED_MANY)
> +		return alloc_pages_bulk_array_preferred_many(gfp,
> +				numa_node_id(), pol, nr_pages, page_array);
> +
> +	return __alloc_pages_bulk(gfp, policy_node(gfp, pol, numa_node_id()),
> +				  policy_nodemask(gfp, pol), nr_pages, NULL,
> +				  page_array);
> +}

Some documentation via code comments would be nice.  If only for
alloc_pages_bulk_array_mempolicy().  Mainly to explain why it exists. 
I suppose the internal functions can be left uncommented if they're
sufficiently obvious?

>  struct folio *folio_alloc(gfp_t gfp, unsigned order)
>  {
>  	struct page *page = alloc_pages(gfp | __GFP_COMP, order);
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index b7ac4a8fe2b3..49adba793f3c 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2856,23 +2856,14 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
>  			 */
>  			nr_pages_request = min(100U, nr_pages - nr_allocated);
>  
> -			if (nid == NUMA_NO_NODE) {
> -				for (i = 0; i < nr_pages_request; i++) {
> -					page = alloc_page(gfp);
> -					if (page)
> -						pages[nr_allocated + i] = page;
> -					else {
> -						nr = i;
> -						break;
> -					}
> -				}
> -				if (i >= nr_pages_request)
> -					nr = nr_pages_request;
> -			} else {
> +			if (nid == NUMA_NO_NODE)
> +				nr = alloc_pages_bulk_array_mempolicy(gfp,
> +							nr_pages_request,
> +							pages + nr_allocated);
> +			else
>  				nr = alloc_pages_bulk_array_node(gfp, nid,
>  							nr_pages_request,
>  							pages + nr_allocated);
> -			}
>  			nr_allocated += nr;
>  			cond_resched();
>