On 20/12/2018 16:52, Aneesh Kumar K.V wrote: > 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@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. >> > > Because we might have failed to isolate all the pages in the first attempt. isolate==migrate? If we failed to migrate, then migrate_pages() returns non zero (positive or negative), we set migrate_allow to false, empty the cma_page_list and repeat but we won't add anything to cma_page_list as migrate_allow==false. If we succeeded to migrate, then we repeat the loop with migrate_allow==true but it does not matter as is_migrate_cma_page() is expected to return false because we just successfully migrated _everything_ so we won't be adding anything to cma_page_list either. What have I missed? -- Alexey
