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

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Message-ID: <20200723061437.GQ32539@MiWiFi-R3L-srv>
Date:   Thu, 23 Jul 2020 14:14:37 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Anshuman Khandual <anshuman.khandual@....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 07/23/20 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.
~~~~~~~~

Thanks
Baoquan