Re: [RFC PATCH v1 2/7] migrate: implement migrate_misplaced_folios_batch

["Huang, Ying" <ying.huang@linux.alibaba.com>]

Bharata B Rao <bharata@amd.com> writes:

> From: Gregory Price <gourry@gourry.net>
>
> A common operation in tiering is to migrate multiple pages at once.

Is it common now?  If so, you can replace some callers of
migrate_misplaced_folio() with migrate_misplaced_folios_batch().

> The migrate_misplaced_folio function requires one call for each

IMHO, migrate_misplaced_folio() is more concise than
migrate_misplaced_folio function.

> individual folio.  Expose a batch-variant of the same call for use
> when doing batch migrations.
>
> Signed-off-by: Gregory Price <gourry@gourry.net>
> Signed-off-by: Bharata B Rao <bharata@amd.com>
> ---
>  include/linux/migrate.h |  6 ++++++
>  mm/migrate.c            | 31 +++++++++++++++++++++++++++++++
>  2 files changed, 37 insertions(+)
>
> diff --git a/include/linux/migrate.h b/include/linux/migrate.h
> index acadd41e0b5c..0593f5869be8 100644
> --- a/include/linux/migrate.h
> +++ b/include/linux/migrate.h
> @@ -107,6 +107,7 @@ static inline int migrate_huge_page_move_mapping(struct address_space *mapping,
>  int migrate_misplaced_folio_prepare(struct folio *folio,
>  		struct vm_area_struct *vma, int node);
>  int migrate_misplaced_folio(struct folio *folio, int node);
> +int migrate_misplaced_folios_batch(struct list_head *foliolist, int node);
>  #else
>  static inline int migrate_misplaced_folio_prepare(struct folio *folio,
>  		struct vm_area_struct *vma, int node)
> @@ -117,6 +118,11 @@ static inline int migrate_misplaced_folio(struct folio *folio, int node)
>  {
>  	return -EAGAIN; /* can't migrate now */
>  }
> +static inline int migrate_misplaced_folios_batch(struct list_head *foliolist,
> +						 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 7e356c0b1b5a..1268a95eda0e 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -2714,5 +2714,36 @@ int migrate_misplaced_folio(struct folio *folio, int node)
>  	BUG_ON(!list_empty(&migratepages));
>  	return nr_remaining ? -EAGAIN : 0;
>  }
> +
> +/*
> + * Batch variant of migrate_misplaced_folio. Attempts to migrate
> + * a folio list to the specified destination.
> + *
> + * Caller is expected to have isolated the folios by calling
> + * migrate_misplaced_folio_prepare(), which will result in an
> + * elevated reference count on the folio.
> + *
> + * This function will un-isolate the folios, dereference them, and
> + * remove them from the list before returning.
> + */
> +int migrate_misplaced_folios_batch(struct list_head *folio_list, int node)

In addition to working on a list of folios instead of single folio, I
found there are some difference about memcg counting between
migrate_misplaced_folios_batch() and migrate_misplace_folio().  Why?

And, can we merge the implementation of two functions to reduce code
duplication?

> +{
> +	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,
Huang, Ying