linux-kernel - Re: [RFC PATCH v0 1/2] migrate: implement migrate_misplaced_folio

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Message-ID: <871psbdbwo.fsf@DESKTOP-5N7EMDA>
Date: Mon, 26 May 2025 16:16:55 +0800
From: "Huang, Ying" <ying.huang@...ux.alibaba.com>
To: Bharata B Rao <bharata@....com>,  <gourry@...rry.net>
Cc: <linux-kernel@...r.kernel.org>,  <linux-mm@...ck.org>,
  <Jonathan.Cameron@...wei.com>,  <dave.hansen@...el.com>,
  <hannes@...xchg.org>,  <mgorman@...hsingularity.net>,
  <mingo@...hat.com>,  <peterz@...radead.org>,  <raghavendra.kt@....com>,
  <riel@...riel.com>,  <rientjes@...gle.com>,  <sj@...nel.org>,
  <weixugc@...gle.com>,  <willy@...radead.org>,  <ziy@...dia.com>,
  <dave@...olabs.net>,  <nifan.cxl@...il.com>,  <joshua.hahnjy@...il.com>,
  <xuezhengchu@...wei.com>,  <yiannis@...corp.com>,
  <akpm@...ux-foundation.org>,  <david@...hat.com>
Subject: Re: [RFC PATCH v0 1/2] migrate: implement
 migrate_misplaced_folio_batch

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

> From: Gregory Price <gourry@...rry.net>
>
> A common operation in tiering is to migrate multiple pages at once.
> The migrate_misplaced_folio function requires one call for each
> individual folio.  Expose a batch-variant of the same call for use
> when doing batch migrations.
>
> Signed-off-by: Gregory Price <gourry@...rry.net>
> Signed-off-by: Bharata B Rao <bharata@....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 aaa2114498d6..c9496adcf192 100644
> --- a/include/linux/migrate.h
> +++ b/include/linux/migrate.h
> @@ -145,6 +145,7 @@ const struct movable_operations *page_movable_ops(struct page *page)
>  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_folio_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)
> @@ -155,6 +156,11 @@ static inline int migrate_misplaced_folio(struct folio *folio, int node)
>  {
>  	return -EAGAIN; /* can't migrate now */
>  }
> +static inline int migrate_misplaced_folio_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 676d9cfc7059..32cc2eafb037 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -2733,5 +2733,36 @@ 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_folio_batch(struct list_head *folio_list, 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 */

migrate_misplaced_folio_batch() looks quite similar as
migrate_misplaced_folio(), can we merge them?

---
Best Regards,
Huang, Ying