On Tue 11-10-16 14:01:41, Minchan Kim wrote: > Hi Michal, > > On Mon, Oct 10, 2016 at 09:41:40AM +0200, Michal Hocko wrote: > > On Fri 07-10-16 23:43:45, Minchan Kim wrote: > > > On Fri, Oct 07, 2016 at 11:09:17AM +0200, Michal Hocko wrote: [...] > > > > @@ -2102,10 +2109,12 @@ static void unreserve_highatomic_pageblock(const struct alloc_context *ac) > > > > set_pageblock_migratetype(page, ac->migratetype); > > > > move_freepages_block(zone, page, ac->migratetype); > > > > spin_unlock_irqrestore(&zone->lock, flags); > > > > - return; > > > > + return true; > > > > > > Such cut-off makes reserved pageblock remained before the OOM. > > > We call it as premature OOM kill. > > > > Not sure I understand. The above should get rid of all atomic reserves > > before we go OOM. We can do it all at once but that sounds too > > The problem is there is race between page freeing path and unreserve > logic so that some pages could be in highatomic free list even though > zone->nr_reserved_highatomic is already zero. Does it make any sense to handle such an unlikely case? > So, at least, it would be better to have a draining step at some point > where was (no_progress_loops == MAX_RECLAIM RETRIES) in my patch. > > Also, your patch makes retry loop greater than MAX_RECLAIM_RETRIES > if unreserve_highatomic_pageblock returns true. Theoretically, > it would make live lock. You might argue it's *really really* rare > but I don't want to add such subtle thing. > Maybe, we could drain when no_progress_loops == MAX_RECLAIM_RETRIES. What would be the scenario when we would really livelock here? How can we have unreserve_highatomic_pageblock returning true for ever? > > aggressive to me. If we just do one at the time we have a chance to > > keep some reserves if the OOM situation is really ephemeral. > > > > Does this patch work in your usecase? > > I didn't test but I guess it works but it has problems I mentioned > above. Please do not make this too over complicated and be practical. I do not really want to dismiss your usecase but I am really not convinced that such a "perfectly fit into all memory" situations are sustainable and justify to make the whole code more complex. I agree that we can at least try to do something to release those reserves but let's do it as simple as possible. -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>