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@xxxxxxxxxxxxx> >> > > ..... >>> + * 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. It should be simple gup_fast() instead of goto and then we won't need goto/migrate_allow. -- Alexey
