On Thu, 29 Dec 2011 17:55:14 -0800 (PST) Hugh Dickins <hughd@xxxxxxxxxx> wrote: > > However, at that time, I think this patch behave > > better than old. If we release and retake zone lock per 14 pages, > > other tasks can easily steal a part of lumpy reclaimed pages. and then > > long latency wrongness will be happen when system is under large page > > memory allocation pressure. That's the reason why I posted very similar patch > > a long time ago. > > Aha, and another good point. Thank you. I hope you understand it better than I :( Long lock hold times and long irq-off times are demonstrable problems which have hurt people in the past. Whereas the someone-stole-my-page issue is theoretical, undemonstrated and unquantified. And for some people, lengthy worst-case latency is a serious problem, doesn't matter whether the system is under memory pressure or not - that simply determines when the worst-case hits. This is not all some handwavy theoretical thing either. If we've gone and introduced serious latency issues, people *will* hit them and treat it as a regression. Now, a way out here is to remove lumpy reclaim (please). And make the problem not come back by promising to never call putback_lru_pages(lots of pages) (how do we do this?). So I think the best way ahead here is to distribute this patch in the same release in which we remove lumpy reclaim (pokes Mel). -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>