linux-kernel - Re: [PATCH 4/3] mm, hugetlb, hwpoison: separate branch for free and in-use hugepage

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Date:   Fri, 15 Apr 2022 08:11:47 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Naoya Horiguchi <naoya.horiguchi@...ux.dev>,
        Miaohe Lin <linmiaohe@...wei.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Yang Shi <shy828301@...il.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        naoya.horiguchi@....com,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/3] mm, hugetlb, hwpoison: separate branch for free and
 in-use hugepage

On 4/14/22 21:18, Naoya Horiguchi wrote:
> From: Naoya Horiguchi <naoya.horiguchi@....com>
> 
> We know that HPageFreed pages should have page refcount 0, so
> get_page_unless_zero() always fails and returns 0.  So explicitly separate
> the branch based on page state for minor optimization and better readability.
> 
> Suggested-by: Mike Kravetz <mike.kravetz@...cle.com>
> Suggested-by: Miaohe Lin <linmiaohe@...wei.com>
> Signed-off-by: Naoya Horiguchi <naoya.horiguchi@....com>
> ---
>  mm/hugetlb.c        | 4 +++-
>  mm/memory-failure.c | 4 +++-
>  2 files changed, 6 insertions(+), 2 deletions(-)

Thank you!

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

> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index e38cbfdf3e61..3638f166e554 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -6786,7 +6786,9 @@ int get_hwpoison_huge_page(struct page *page, bool *hugetlb)
>  	spin_lock_irq(&hugetlb_lock);
>  	if (PageHeadHuge(page)) {
>  		*hugetlb = true;
> -		if (HPageFreed(page) || HPageMigratable(page))
> +		if (HPageFreed(page))
> +			ret = 0;
> +		else if (HPageMigratable(page))
>  			ret = get_page_unless_zero(page);
>  		else
>  			ret = -EBUSY;
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 5e3ad640f5bb..661079a37f29 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1517,7 +1517,9 @@ int __get_huge_page_for_hwpoison(unsigned long pfn, int flags)
>  	if (flags & MF_COUNT_INCREASED) {
>  		ret = 1;
>  		count_increased = true;
> -	} else if (HPageFreed(head) || HPageMigratable(head)) {
> +	} else if (HPageFreed(head)) {
> +		ret = 0;
> +	} else if (HPageMigratable(head)) {
>  		ret = get_page_unless_zero(head);
>  		if (ret)
>  			count_increased = true;