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

[John Hubbard]

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.


thanks,
--
John Hubbard
NVIDIA