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Subject: Re: [PATCH v4] mm: fix is_pinnable_page against on cma page
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To:     Minchan Kim <minchan@kernel.org>
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From:   John Hubbard <jhubbard@nvidia.com>
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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