Messages in this thread | | | Subject | Re: [PATCH V5 1/3] mm: Add get_user_pages_cma_migrate | From | "Aneesh Kumar K.V" <> | Date | Thu, 20 Dec 2018 11:22:32 +0530 |
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On 12/20/18 11:18 AM, Alexey Kardashevskiy wrote: > > > On 20/12/2018 16:22, Aneesh Kumar K.V wrote: >> On 12/20/18 9:49 AM, Alexey Kardashevskiy wrote: >>> >>> >>> On 19/12/2018 14:40, Aneesh Kumar K.V wrote: >>>> This helper does a get_user_pages_fast and if it find pages in the >>>> CMA area >>>> it will try to migrate them before taking page reference. This makes >>>> sure that >>>> we don't keep non-movable pages (due to page reference count) in the >>>> CMA area. >>>> Not able to move pages out of CMA area result in CMA allocation >>>> failures. >>>> >>>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> >>> >> >> ..... >>>> + * We did migrate all the pages, Try to get the page >>>> references again >>>> + * migrating any new CMA pages which we failed to isolate >>>> earlier. >>>> + */ >>>> + drain_allow = true; >>>> + goto get_user_again; >>> >>> >>> So it is possible to have pages pinned, then successfully migrated >>> (migrate_pages() returned 0), then pinned again, then some pages may end >>> up in CMA again and migrate again and nothing seems to prevent this loop >>> from being endless. What do I miss? >>> >> >> pages used as target page for migration won't be allocated from CMA region. > > > Then migrate_allow should be set to "false" regardless what > migrate_pages() returned and then I am totally missing the point of this > goto and going through the loop again even when we know for sure it > won't do literally anything but checking is_migrate_cma_page() even > though we know pages won't be allocated from CMA. >
Because we might have failed to isolate all the pages in the first attempt.
-aneesh
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