Jason Gunthorpe <jgg@xxxxxxxxxx> writes:
> On Tue, Aug 16, 2022 at 03:29:20PM +1000, Alistair Popple wrote:
>
>> >> +static long check_and_migrate_movable_pages(unsigned long nr_pages,
>> >> + struct page **pages)
>> >> +{
>> >> + int ret;
>> >> + unsigned long collected;
>> >> + LIST_HEAD(movable_page_list);
>> >> +
>> >> + collected = collect_longterm_unpinnable_pages(&movable_page_list, nr_pages, pages);
>> >> + if (!collected)
>> >> + return 0;
>> >> +
>> >> + ret = migrate_longterm_unpinnable_pages(&movable_page_list, nr_pages, pages);
>> >> + if (!ret)
>> >> + return -EAGAIN;
>> >> + else
>> >> + return ret;
>> >
>> > I would drop the else path and just return zero
>>
>> Unless I've misunderstood you I don't think that's correct though.
>> check_and_migrate_movable_pages() needs to return one of 3 conditions:
>>
>> - 0: All pages are in the correct zone and are still pinned (ie. "success").
>> - -EAGAIN: Some pages were migrated, all pages need re-pinning.
>> - errno: Migration failed, pins were dropped and PUP should fail.
>>
>> John's suggested comment update spells this out more clearly.
>
> But that is not what it does..
>
> if (!ret) == if (ret != 0)
Huh? Unless I'm misinterpretting you or am really behind on coffee
if (!ret) is equivalent to if (ret == 0), not if (ret != 0).
Ie:
if (ret == 0)
return -EAGAIN;
else
return !0;
Thus we will never return 0 from the above snippet.
> return -EAGAIN
> thus ret == 0
> return ret == return 0
>
> Jason
