linux-kernel - Re: [PATCH] mm/hugetlb: Remove redundant VM_BUG_ON_PAGE on putback_active

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Date:   Mon, 8 Feb 2021 17:26:08 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Miaohe Lin <linmiaohe@...wei.com>, akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/hugetlb: Remove redundant VM_BUG_ON_PAGE on
 putback_active_hugepage()

On 2/8/21 12:37 AM, Miaohe Lin wrote:
> PageHead(page) is implicitly checked in set_page_huge_active() via the
> PageHeadHuge(page) check. So remove this explicit one.

I do not disagree with the code change.  However, this commit message
is not accurate.  set_page_huge_active() no longer exists in the tree
you are changing.  It was replaced with SetHPageMigratable.  Also, the
VM_BUG_ON_PAGE(!PageHeadHuge(page), page) was removed in the process.
So, there is no redundant check.

However, a quick audit of calling code reveals that all callers know they
are operating on a hugetlb head page.
-- 
Mike Kravetz

> 
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  mm/hugetlb.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 6cdb59d8f663..bbbe013a3a2d 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -5577,7 +5577,6 @@ bool isolate_huge_page(struct page *page, struct list_head *list)
>  
>  void putback_active_hugepage(struct page *page)
>  {
> -	VM_BUG_ON_PAGE(!PageHead(page), page);
>  	spin_lock(&hugetlb_lock);
>  	SetHPageMigratable(page);
>  	list_move_tail(&page->lru, &(page_hstate(page))->hugepage_activelist);
>