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

John Hubbard
2022-05-11T23:12:49Z

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