linux-kernel - Re: [PATCH v4] mm: fix is_pinnable

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Date:   Wed, 11 May 2022 16:15:17 -0700
From:   Minchan Kim <minchan@...nel.org>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        John Dias <joaodias@...gle.com>,
        David Hildenbrand <david@...hat.com>
Subject: Re: [PATCH v4] mm: fix is_pinnable_page against on cma page

On Wed, May 11, 2022 at 04:13:10PM -0700, John Hubbard wrote:
> On 5/11/22 16:08, Minchan Kim wrote:
> > > OK, so the code checks the wrong item each time. But the code really
> > > only needs to know "is either _CMA or _ISOLATE set?". And so you
> > 
> > Yes.
> > 
> > > can just sidestep the entire question by writing it like this:
> > > 
> > > int mt = get_pageblock_migratetype(page);
> > > 
> > > if (mt & (MIGRATE_ISOLATE | MIGRATE_CMA))
> > > 	return false;
> > 
> > I am confused. Isn't it same question?
> > 
> >                                                      set_pageblock_migratetype(MIGRATE_ISOLATE)
> > if (get_pageblock_migrate(page) & MIGRATE_CMA)
> > 
> >                                                      set_pageblock_migratetype(MIGRATE_CMA)
> > 
> > if (get_pageblock_migrate(page) & MIGRATE_ISOLATE)
> 
> Well no, because the "&" operation is a single operation on the CPU, and
> isn't going to get split up like that.

Oh, if that's true, yeah, I could live with it.

Thanks, let me post next revision with commenting about that.