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SubjectRe: [PATCH] mm/gup: remove unnecessary check against CMA in __gup_longterm_locked()
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On 6/4/19 12:56 PM, Pingfan Liu wrote:
> The PF_MEMALLOC_NOCMA is set by memalloc_nocma_save(), which is finally
> cast to ~_GFP_MOVABLE. So __get_user_pages_locked() will get pages from
> non CMA area and pin them. There is no need to
> check_and_migrate_cma_pages().


That is not completely correct. We can fault in that pages outside
get_user_pages_longterm at which point those pages can get allocated
from CMA region. memalloc_nocma_save() as added as an optimization to
avoid unnecessary page migration.


-aneesh

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