On Tue 24-11-15 15:44:48, Andrew Morton wrote: [...] > > Even though we haven't seen bug reports in the past I would suggest > > backporting this to the stable trees. The issue is present since we have > > stopped useing congestion_wait in the retry loop because WQ concurrency > > is older as well as vmstat worqueue based refresh AFAICS. > > hm, I'm reluctant. If the patch fixes something that real people are > really hurting from then yes. But I suspect this is just one fly-swat > amongst many. Arkadiusz was seeing reclaim issues [1] on 4.1 kernel. I didn't have time to look deeper in that report but vmstat counters seemed terribly outdated and the issue went away when this patch was used. The thing is that there were others in the bundle so it is not 100% clear whether the patch alone helped or it was just a part of the puzzle. Anyway I think that the issue is not solely theoretical. WQ_MEM_RECLAIM is simply not working if the allocation path doesn't sleep currently and my understanding of what Tejun claims [2] is that that reimplementing WQ concurrency would be too intrusive and lacks sufficient justification because other kernel paths do sleep. This patch tries to reduce the sleep only to worker threads which should not cause any problems to regular tasks. I am open to any other suggestions. I do not like artificial sleep as well but this sounds like the most practical way to go now. [1] http://lkml.kernel.org/r/201511102313.36685.arekm@xxxxxxxx [2] http://lkml.kernel.org/r/20151106001648.GA18183@xxxxxxxxxxxxxxx -- 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>