Re: [PATCH 2/9] mm/page_alloc: Add a bulk page allocator

Vlastimil Babka
2021-04-12T10:22:02Z

On 3/25/21 12:42 PM, Mel Gorman wrote:
> This patch adds a new page allocator interface via alloc_pages_bulk,
> and __alloc_pages_bulk_nodemask. A caller requests a number of pages
> to be allocated and added to a list.
>
> The API is not guaranteed to return the requested number of pages and
> may fail if the preferred allocation zone has limited free memory, the
> cpuset changes during the allocation or page debugging decides to fail
> an allocation. It's up to the caller to request more pages in batch
> if necessary.
>
> Note that this implementation is not very efficient and could be improved
> but it would require refactoring. The intent is to make it available early
> to determine what semantics are required by different callers. Once the
> full semantics are nailed down, it can be refactored.
>
> Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
> Acked-by: Vlastimil Babka <vbabka@suse.cz>
> ---
> include/linux/gfp.h | 11 +++++
> mm/page_alloc.c | 118 ++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 129 insertions(+)
>
> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> index 0a88f84b08f4..4a304fd39916 100644
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -518,6 +518,17 @@ static inline int arch_make_page_accessible(struct page *page)
> struct page *__alloc_pages(gfp_t gfp, unsigned int order, int preferred_nid,
> nodemask_t *nodemask);
>
> +int __alloc_pages_bulk(gfp_t gfp, int preferred_nid,
> + nodemask_t *nodemask, int nr_pages,
> + struct list_head *list);
> +
> +/* Bulk allocate order-0 pages */
> +static inline unsigned long
> +alloc_pages_bulk(gfp_t gfp, unsigned long nr_pages, struct list_head *list)
> +{
> + return __alloc_pages_bulk(gfp, numa_mem_id(), NULL, nr_pages, list);
> +}
> +
> /*
> * Allocate pages, preferring the node given as nid. The node must be valid and
> * online. For more general interface, see alloc_pages_node().
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 8a3e13277e22..eb547470a7e4 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4965,6 +4965,124 @@ static inline bool prepare_alloc_pages(gfp_t gfp_mask, unsigned int order,
> return true;
> }
>
> +/*
> + * __alloc_pages_bulk - Allocate a number of order-0 pages to a list
> + * @gfp: GFP flags for the allocation
> + * @preferred_nid: The preferred NUMA node ID to allocate from
> + * @nodemask: Set of nodes to allocate from, may be NULL
> + * @nr_pages: The number of pages desired on the list
> + * @page_list: List to store the allocated pages
> + *
> + * This is a batched version of the page allocator that attempts to
> + * allocate nr_pages quickly and add them to a list.
> + *
> + * Returns the number of pages on the list.
> + */
> +int __alloc_pages_bulk(gfp_t gfp, int preferred_nid,
> + nodemask_t *nodemask, int nr_pages,
> + struct list_head *page_list)
> +{
> + struct page *page;
> + unsigned long flags;
> + struct zone *zone;
> + struct zoneref *z;
> + struct per_cpu_pages *pcp;
> + struct list_head *pcp_list;
> + struct alloc_context ac;
> + gfp_t alloc_gfp;
> + unsigned int alloc_flags;

Was going to complain that this is not set to ALLOC_WMARK_LOW. Must be faster
next time...

> + int allocated = 0;
> +
> + if (WARN_ON_ONCE(nr_pages <= 0))
> + return 0;
> +
> + /* Use the single page allocator for one page. */
> + if (nr_pages == 1)
> + goto failed;
> +
> + /* May set ALLOC_NOFRAGMENT, fragmentation will return 1 page. */

I don't understand this comment. Only alloc_flags_nofragment() sets this flag
and we don't use it here?

> + gfp &= gfp_allowed_mask;
> + alloc_gfp = gfp;
> + if (!prepare_alloc_pages(gfp, 0, preferred_nid, nodemask, &ac, &alloc_gfp, &alloc_flags))
> + return 0;
> + gfp = alloc_gfp;
> +
> + /* Find an allowed local zone that meets the high watermark. */

Should it say "low watermark"?

Vlastimil