Re: [RFC PATCH 0/5] Accelerate page migration with batching and multi threads

[Zi Yan <ziy@nvidia.com>]

On 3 Jan 2025, at 14:17, Gregory Price wrote:

> On Fri, Jan 03, 2025 at 12:24:14PM -0500, Zi Yan wrote:
>> Hi all,
>>
>> This patchset accelerates page migration by batching folio copy operations and
>> using multiple CPU threads and is based on Shivank's Enhancements to Page
>> Migration with Batch Offloading via DMA patchset[1] and my original accelerate
>> page migration patchset[2]. It is on top of mm-everything-2025-01-03-05-59.
>> The last patch is for testing purpose and should not be considered.
>>
>
> This is well timed as I've been testing a batch-migration variant of
> migrate_misplaced_folio for my pagecache promotion work (attached).
>
> I will add this to my pagecache branch and give it a test at some point.

Great. Thanks.

>
> Quick question: is the multi-threaded movement supported in the context
> of task_work?  i.e. in which context is the multi-threaded path
> safe/unsafe? (inline in a syscall, async only, etc).

It should work in any context, like syscall, memory compaction, and so on,
since it just distributes memcpy to different CPUs using workqueue.

>
> ~Gregory
>
> ---
>
> diff --git a/include/linux/migrate.h b/include/linux/migrate.h
> index 9438cc7c2aeb..17baf63964c0 100644
> --- a/include/linux/migrate.h
> +++ b/include/linux/migrate.h
> @@ -146,6 +146,9 @@ int migrate_misplaced_folio_prepare(struct folio *folio,
>                 struct vm_area_struct *vma, int node);
>  int migrate_misplaced_folio(struct folio *folio, struct vm_area_struct *vma,
>                            int node);
> +int migrate_misplaced_folio_batch(struct list_head *foliolist,
> +                                 struct vm_area_struct *vma,
> +                                 int node);
>  #else
>  static inline int migrate_misplaced_folio_prepare(struct folio *folio,
>                 struct vm_area_struct *vma, int node)
> @@ -157,6 +160,12 @@ static inline int migrate_misplaced_folio(struct folio *folio,
>  {
>         return -EAGAIN; /* can't migrate now */
>  }
> +int migrate_misplaced_folio_batch(struct list_head *foliolist,
> +                                 struct vm_area_struct *vma,
> +                                 int node)
> +{
> +       return -EAGAIN; /* can't migrate now */
> +}
>  #endif /* CONFIG_NUMA_BALANCING */
>
>  #ifdef CONFIG_MIGRATION
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 459f396f7bc1..454fd93c4cc7 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -2608,5 +2608,27 @@ int migrate_misplaced_folio(struct folio *folio, struct vm_area_struct *vma,
>         BUG_ON(!list_empty(&migratepages));
>         return nr_remaining ? -EAGAIN : 0;
>  }
> +
> +int migrate_misplaced_folio_batch(struct list_head *folio_list,
> +                                 struct vm_area_struct *vma,
> +                                 int node)
> +{
> +       pg_data_t *pgdat = NODE_DATA(node);
> +       unsigned int nr_succeeded;
> +       int nr_remaining;
> +
> +       nr_remaining = migrate_pages(folio_list, alloc_misplaced_dst_folio,
> +                                    NULL, node, MIGRATE_ASYNC,
> +                                    MR_NUMA_MISPLACED, &nr_succeeded);
> +       if (nr_remaining)
> +               putback_movable_pages(folio_list);
> +
> +       if (nr_succeeded) {
> +               count_vm_numa_events(NUMA_PAGE_MIGRATE, nr_succeeded);
> +               mod_node_page_state(pgdat, PGPROMOTE_SUCCESS, nr_succeeded);
> +       }
> +       BUG_ON(!list_empty(folio_list));
> +       return nr_remaining ? -EAGAIN : 0;
> +}
>  #endif /* CONFIG_NUMA_BALANCING */
>  #endif /* CONFIG_NUMA */


Best Regards,
Yan, Zi