linux-kernel - Re: [PATCH v2 2/4] mm/hugetlb.c: Remove the unnecessary non_swap

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Message-ID: <f66035ea-abfa-2523-8df5-ceb3599c9395@arm.com>
Date:   Thu, 23 Jul 2020 10:36:14 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Baoquan He <bhe@...hat.com>, linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, mike.kravetz@...cle.com, david@...hat.com,
        akpm@...ux-foundation.org
Subject: Re: [PATCH v2 2/4] mm/hugetlb.c: Remove the unnecessary
 non_swap_entry()



On 07/23/2020 08:52 AM, Baoquan He wrote:
> The checking is_migration_entry() and is_hwpoison_entry() are stricter
> than non_swap_entry(), means they have covered the conditional check
> which non_swap_entry() is doing.

They are no stricter as such but implicitly contains non_swap_entry() in itself.
If a swap entry tests positive for either is_[migration|hwpoison]_entry(), then
its swap_type() is among SWP_MIGRATION_READ, SWP_MIGRATION_WRITE and SWP_HWPOISON.
All these types >= MAX_SWAPFILES, exactly what is asserted with non_swap_entry().

> 
> Hence remove the unnecessary non_swap_entry() in is_hugetlb_entry_migration()
> and is_hugetlb_entry_hwpoisoned() to simplify code.
> 
> Signed-off-by: Baoquan He <bhe@...hat.com>
> Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>
> Reviewed-by: David Hildenbrand <david@...hat.com>
> ---
>  mm/hugetlb.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 3569e731e66b..c14837854392 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -3748,7 +3748,7 @@ bool is_hugetlb_entry_migration(pte_t pte)
>  	if (huge_pte_none(pte) || pte_present(pte))
>  		return false;
>  	swp = pte_to_swp_entry(pte);
> -	if (non_swap_entry(swp) && is_migration_entry(swp))
> +	if (is_migration_entry(swp))
>  		return true;
>  	else
>  		return false;
> @@ -3761,7 +3761,7 @@ static bool is_hugetlb_entry_hwpoisoned(pte_t pte)
>  	if (huge_pte_none(pte) || pte_present(pte))
>  		return false;
>  	swp = pte_to_swp_entry(pte);
> -	if (non_swap_entry(swp) && is_hwpoison_entry(swp))
> +	if (is_hwpoison_entry(swp))
>  		return true;
>  	else
>  		return false;
> 

It would be better if the commit message contains details about
the existing redundant check. But either way.

Reviewed-by: Anshuman Khandual <anshuman.khandual@....com>