linux-kernel - Re: [PATCH v2 3/4] mm: hugetlb: change to return bool for isolate

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Date:   Tue, 14 Feb 2023 10:21:31 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     SeongJae Park <sj@...nel.org>
Cc:     Baolin Wang <baolin.wang@...ux.alibaba.com>,
        akpm@...ux-foundation.org, torvalds@...ux-foundation.org,
        hannes@...xchg.org, mhocko@...nel.org, roman.gushchin@...ux.dev,
        shakeelb@...gle.com, muchun.song@...ux.dev,
        naoya.horiguchi@....com, linmiaohe@...wei.com, david@...hat.com,
        osalvador@...e.de, willy@...radead.org, damon@...ts.linux.dev,
        cgroups@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/4] mm: hugetlb: change to return bool for
 isolate_hugetlb()

On 02/14/23 18:07, SeongJae Park wrote:
> On Tue, 14 Feb 2023 18:03:24 +0000 SeongJae Park <sj@...nel.org> wrote:
> 
> > On Tue, 14 Feb 2023 21:59:31 +0800 Baolin Wang <baolin.wang@...ux.alibaba.com> wrote:
> > 
> > > Now the isolate_hugetlb() only returns 0 or -EBUSY, and most users did not
> > > care about the negative value, thus we can convert the isolate_hugetlb()
> > > to return a boolean value to make code more clear when checking the
> > > hugetlb isolation state. Moreover converts 2 users which will consider
> > > the negative value returned by isolate_hugetlb().
> > > 
> > > No functional changes intended.
> > > 
> > > Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> > > ---
> > >  include/linux/hugetlb.h |  6 +++---
> > >  mm/hugetlb.c            | 12 ++++++++----
> > >  mm/memory-failure.c     |  2 +-
> > >  mm/mempolicy.c          |  2 +-
> > >  mm/migrate.c            |  2 +-
> > >  5 files changed, 14 insertions(+), 10 deletions(-)
> > > 
> > > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> > > index df6dd624ccfe..5f5e4177b2e0 100644
> [...]
> > > diff --git a/mm/migrate.c b/mm/migrate.c
> > > index 53010a142e7f..c5136fa48638 100644
> > > --- a/mm/migrate.c
> > > +++ b/mm/migrate.c
> > > @@ -2128,7 +2128,7 @@ static int add_page_for_migration(struct mm_struct *mm, unsigned long addr,
> > >  		if (PageHead(page)) {
> > >  			err = isolate_hugetlb(page_folio(page), pagelist);
> > >  			if (!err)
> > > -				err = 1;
> > > +				err = -EBUSY;
> > 
> > Again, I think this is confusing.  'err' is 'bool', not 'int'.
> 
> I mean, 'err' is not 'bool' but 'int', sorry.  See? This confuses me ;)
> 

Yes,
in the case here (and elsewhere) I like David's suggestion of using a separate
bool such as 'isolated' to capture the return value of the isolate function.
Then, the statement:

	err = isolated ? 0 : -EBUSY;

would be pretty clear.
-- 
Mike Kravetz