linux-kernel - Re: [PATCH mm-unstable 8/8] mm/hugetlb: convert demote_free_huge

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Message-ID: <Y7jGyH9Atv3sPjcZ@monkey>
Date:   Fri, 6 Jan 2023 17:11:36 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Sidhartha Kumar <sidhartha.kumar@...cle.com>, willy@...radead.org
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, songmuchun@...edance.com,
        tsahu@...ux.ibm.com, jhubbard@...dia.com
Subject: Re: [PATCH mm-unstable 8/8] mm/hugetlb: convert
 demote_free_huge_page to folios

On 01/03/23 13:13, Sidhartha Kumar wrote:
> Change demote_free_huge_page to demote_free_hugetlb_folio() and change
> demote_pool_huge_page() pass in a folio.
> 
> Signed-off-by: Sidhartha Kumar <sidhartha.kumar@...cle.com>
> ---
>  mm/hugetlb.c | 31 ++++++++++++++++---------------
>  1 file changed, 16 insertions(+), 15 deletions(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 2bb69b098117..a89728c6987d 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -3438,12 +3438,12 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
>  	return 0;
>  }
>  
> -static int demote_free_huge_page(struct hstate *h, struct page *page)
> +static int demote_free_hugetlb_folio(struct hstate *h, struct folio *folio)
>  {
> -	int i, nid = page_to_nid(page);
> +	int i, nid = folio_nid(folio);
>  	struct hstate *target_hstate;
> -	struct folio *folio = page_folio(page);
>  	struct page *subpage;
> +	struct folio *subfolio;
>  	int rc = 0;
>  
>  	target_hstate = size_to_hstate(PAGE_SIZE << h->demote_order);
> @@ -3451,18 +3451,18 @@ static int demote_free_huge_page(struct hstate *h, struct page *page)
>  	remove_hugetlb_folio_for_demote(h, folio, false);
>  	spin_unlock_irq(&hugetlb_lock);
>  
> -	rc = hugetlb_vmemmap_restore(h, page);
> +	rc = hugetlb_vmemmap_restore(h, &folio->page);
>  	if (rc) {
> -		/* Allocation of vmemmmap failed, we can not demote page */
> +		/* Allocation of vmemmmap failed, we can not demote folio */
>  		spin_lock_irq(&hugetlb_lock);
> -		set_page_refcounted(page);
> -		add_hugetlb_folio(h, page_folio(page), false);
> +		folio_ref_unfreeze(folio, 1);
> +		add_hugetlb_folio(h, folio, false);
>  		return rc;
>  	}
>  
>  	/*
>  	 * Use destroy_compound_hugetlb_folio_for_demote for all huge page
> -	 * sizes as it will not ref count pages.
> +	 * sizes as it will not ref count folios.
>  	 */
>  	destroy_compound_hugetlb_folio_for_demote(folio, huge_page_order(h));
>  
> @@ -3477,15 +3477,15 @@ static int demote_free_huge_page(struct hstate *h, struct page *page)
>  	mutex_lock(&target_hstate->resize_lock);
>  	for (i = 0; i < pages_per_huge_page(h);
>  				i += pages_per_huge_page(target_hstate)) {
> -		subpage = nth_page(page, i);
> -		folio = page_folio(subpage);
> +		subpage = folio_page(folio, i);
> +		subfolio = page_folio(subpage);

No problems with the code, but I am not in love with the name subfolio.
I know it is patterned after 'subpage'.  For better or worse, the term
subpage is used throughout the kernel.  This would be the first usage of
the term 'subfolio'.

Matthew do you have any comments on the naming?  It is local to hugetlb,
but I would hate to see use of the term subfolio based on its introduction
here.
-- 
Mike Kravetz


>  		if (hstate_is_gigantic(target_hstate))
> -			prep_compound_gigantic_folio_for_demote(folio,
> +			prep_compound_gigantic_folio_for_demote(subfolio,
>  							target_hstate->order);
>  		else
>  			prep_compound_page(subpage, target_hstate->order);
> -		set_page_private(subpage, 0);
> -		prep_new_hugetlb_folio(target_hstate, folio, nid);
> +		folio_change_private(subfolio, NULL);
> +		prep_new_hugetlb_folio(target_hstate, subfolio, nid);
>  		free_huge_page(subpage);
>  	}
>  	mutex_unlock(&target_hstate->resize_lock);
>