Re: [PATCH 07/12] hugetlb: perform vmemmap restoration on a list of pages

[Muchun Song <muchun.song@linux.dev>]

On 2023/8/26 03:04, Mike Kravetz wrote:
> When removing hugetlb pages from the pool, we first create a list
> of removed pages and then free those pages back to low level allocators.
> Part of the 'freeing process' is to restore vmemmap for all base pages
> if necessary.  Pass this list of pages to a new routine
> hugetlb_vmemmap_restore_folios() so that vmemmap restoration can be
> performed in bulk.
>
> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
> ---
>   mm/hugetlb.c         | 3 +++
>   mm/hugetlb_vmemmap.c | 8 ++++++++
>   mm/hugetlb_vmemmap.h | 6 ++++++
>   3 files changed, 17 insertions(+)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 3133dbd89696..1bde5e234d5c 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1833,6 +1833,9 @@ static void update_and_free_pages_bulk(struct hstate *h, struct list_head *list)
>   {
>   	struct folio *folio, *t_folio;
>   
> +	/* First restore vmemmap for all pages on list. */
> +	hugetlb_vmemmap_restore_folios(h, list);
> +
>   	list_for_each_entry_safe(folio, t_folio, list, lru) {
>   		update_and_free_hugetlb_folio(h, folio, false);
>   		cond_resched();
> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
> index 147018a504a6..d5e6b6c76dce 100644
> --- a/mm/hugetlb_vmemmap.c
> +++ b/mm/hugetlb_vmemmap.c
> @@ -479,6 +479,14 @@ int hugetlb_vmemmap_restore(const struct hstate *h, struct page *head)
>   	return ret;
>   }
>   

Because it is a void function, I'd like to add a comment here like:

     This function only tries to restore a list of folios' vmemmap pages and
     does not guarantee that the restoration will succeed after it returns.

Thanks.

> +void hugetlb_vmemmap_restore_folios(const struct hstate *h, struct list_head *folio_list)
> +{
> +	struct folio *folio;
> +
> +	list_for_each_entry(folio, folio_list, lru)
> +		hugetlb_vmemmap_restore(h, &folio->page);
> +}
> +
>   /* Return true iff a HugeTLB whose vmemmap should and can be optimized. */
>   static bool vmemmap_should_optimize(const struct hstate *h, const struct page *head)
>   {
> diff --git a/mm/hugetlb_vmemmap.h b/mm/hugetlb_vmemmap.h
> index 036494e040ca..b7074672ceb2 100644
> --- a/mm/hugetlb_vmemmap.h
> +++ b/mm/hugetlb_vmemmap.h
> @@ -12,6 +12,7 @@
>   
>   #ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
>   int hugetlb_vmemmap_restore(const struct hstate *h, struct page *head);
> +void hugetlb_vmemmap_restore_folios(const struct hstate *h, struct list_head *folio_list);
>   void hugetlb_vmemmap_optimize(const struct hstate *h, struct page *head);
>   void hugetlb_vmemmap_optimize_folios(struct hstate *h, struct list_head *folio_list);
>   
> @@ -44,6 +45,11 @@ static inline int hugetlb_vmemmap_restore(const struct hstate *h, struct page *h
>   	return 0;
>   }
>   
> +static inline void hugetlb_vmemmap_restore_folios(const struct hstate *h, struct list_head *folio_list)
> +{
> +	return 0;
> +}
> +
>   static inline void hugetlb_vmemmap_optimize(const struct hstate *h, struct page *head)
>   {
>   }