linux-kernel - Re: [PATCH 3/4] mm: hugetlb_vmemmap: move PageVmemmapSelfHosted() check to split_vmemmap_huge

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Date:   Mon, 4 Dec 2023 15:27:28 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     muchun.song@...ux.dev, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] mm: hugetlb_vmemmap: move PageVmemmapSelfHosted()
 check to split_vmemmap_huge_pmd()

On 11/27/23 16:46, Muchun Song wrote:
> To check a page whether it is self-hosted needs to traverse the page table (e.g.
> pmd_off_k()), however, we already have done this in the next calling of
> vmemmap_remap_range().  Moving PageVmemmapSelfHosted() check to vmemmap_pmd_entry()
> could simplify the code a bit.
> 
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> ---
>  mm/hugetlb_vmemmap.c | 70 +++++++++++++++-----------------------------
>  1 file changed, 24 insertions(+), 46 deletions(-)
> 
> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
> index ef14356855d13..ce920ca6c90ee 100644
> --- a/mm/hugetlb_vmemmap.c
> +++ b/mm/hugetlb_vmemmap.c
> @@ -95,6 +95,7 @@ static int vmemmap_split_pmd(pmd_t *pmd, struct page *head, unsigned long start,
>  static int vmemmap_pmd_entry(pmd_t *pmd, unsigned long addr,
>  			     unsigned long next, struct mm_walk *walk)
>  {
> +	int ret = 0;
>  	struct page *head;
>  	struct vmemmap_remap_walk *vmemmap_walk = walk->private;
>  
> @@ -104,9 +105,30 @@ static int vmemmap_pmd_entry(pmd_t *pmd, unsigned long addr,
>  
>  	spin_lock(&init_mm.page_table_lock);
>  	head = pmd_leaf(*pmd) ? pmd_page(*pmd) : NULL;

I was going to ask why you dropped the:
	if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
However, without the extra page table reads it really is not necessary.

Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>
-- 
Mike Kravetz