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

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Message-ID: <7c0d19e9-4f90-9f74-d364-4d877ccf67f9@arm.com>
Date:   Thu, 23 Jul 2020 14:22:58 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Baoquan He <bhe@...hat.com>
Cc:     linux-kernel@...r.kernel.org, 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 11:44 AM, Baoquan He wrote:
> On 07/23/20 at 10:36am, Anshuman Khandual wrote:
>>
>>
>> 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.
> 
> Thanks for your advice. Do you think updating the log as below is OK?
> 
> ~~~~~~~~
> 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().
> 
> So the checking non_swap_entry() in is_hugetlb_entry_migration() and
> is_hugetlb_entry_hwpoisoned() is redundant.
> 
> Let's remove it to optimize code.
> ~~~~~~~~

Something like above would be good.