Re: [PATCH v4] mm: fix is_pinnable_page against on cma page

[Minchan Kim]

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.