On Mon, Oct 12, 2015 at 8:25 AM, Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> wrote: > > I examined this hang up using additional debug printk() patch. And it was > observed that when this silent hang up occurs, zone_reclaimable() called from > shrink_zones() called from a __GFP_FS memory allocation request is returning > true forever. Since the __GFP_FS memory allocation request can never call > out_of_memory() due to did_some_progree > 0, the system will silently hang up > with 100% CPU usage. I wouldn't blame the zones_reclaimable() logic itself, but yeah, that looks bad. So the do_try_to_free_pages() logic that does that /* Any of the zones still reclaimable? Don't OOM. */ if (zones_reclaimable) return 1; is rather dubious. The history of that odd line is pretty dubious too: it used to be that we would return success if "shrink_zones()" succeeded or if "nr_reclaimed" was non-zero, but that "shrink_zones()" logic got rewritten, and I don't think the current situation is all that sane. And returning 1 there is actively misleading to callers, since it makes them think that it made progress. So I think you should look at what happens if you just remove that illogical and misleading return value. HOWEVER. I think that it's very true that we have then tuned all our *other* heuristics for taking this thing into account, so I suspect that we'll find that we'll need to tweak other places. But this crazy "let's say that we made progress even when we didn't" thing looks just wrong. In particular, I think that you'll find that you will have to change the heuristics in __alloc_pages_slowpath() where we currently do if ((did_some_progress && order <= PAGE_ALLOC_COSTLY_ORDER) || .. when the "did_some_progress" logic changes that radically. Because while the current return value looks insane, all the other testing and tweaking has been done with that very odd return value in place. Linus -- 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>