On Wed 17-03-21 15:42:43, David Hildenbrand wrote: > On 17.03.21 15:05, Michal Hocko wrote: > > On Wed 17-03-21 12:12:47, Oscar Salvador wrote: > > > Currently, __alloc_contig_migrate_range can generate -EINTR, -ENOMEM or -EBUSY, > > > and report them down the chain. > > > The problem is that when migrate_pages() reports -ENOMEM, we keep going till we > > > exhaust all the try-attempts (5 at the moment) instead of bailing out. > > > > > > migrate_pages() bails out right away on -ENOMEM because it is considered a fatal > > > error. Do the same here instead of keep going and retrying. > > > > I suspect this is not really a real life problem, right? The allocation > > would be more costly in the end but this is to be expected under a heavy > > memory pressure. > > > > That being said, bailing out early makes sense to me. But now that > > you've made me look into the migrate_pages excellent error state reporting > > I suspect we have a bug here. Note the > > "Returns the number of pages that were not migrated, or an error code." > > > > but I do not see putback_movable_pages for ret > 0 so it seems we might > > leak some pages. > > At least in __alloc_contig_migrate_range() we seem to always leave the loop > with ret <= 0 and do a putback_movable_pages() with ret < 0. > > Which code are you referring to? OK, my bad. I have managed to confuse myself around the retry bailout which indeed overrides the return value. So there is no bug. Sorry about the noise but I still believe making migrate_pages less tricky with error handling would be an improvement. Thanks! -- Michal Hocko SUSE Labs
