Messages in this thread | | | Date | Wed, 25 Jul 2018 13:11:15 -0500 | From | John Allen <> | Subject | Infinite looping observed in __offline_pages |
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Hi All,
Under heavy stress and constant memory hot add/remove, I have observed the following loop to occasionally loop infinitely:
mm/memory_hotplug.c:__offline_pages
repeat: /* start memory hot removal */ ret = -EINTR; if (signal_pending(current)) goto failed_removal;
cond_resched(); lru_add_drain_all(); drain_all_pages(zone);
pfn = scan_movable_pages(start_pfn, end_pfn); if (pfn) { /* We have movable pages */ ret = do_migrate_range(pfn, end_pfn); goto repeat; }
What appears to be happening in this case is that do_migrate_range returns a failure code which is being ignored. The failure is stemming from migrate_pages returning "1" which I'm guessing is the result of us hitting the following case:
mm/migrate.c: migrate_pages
default: /* * Permanent failure (-EBUSY, -ENOSYS, etc.): * unlike -EAGAIN case, the failed page is * removed from migration page list and not * retried in the next outer loop. */ nr_failed++; break; }
Does a failure in do_migrate_range indicate that the range is unmigratable and the loop in __offline_pages should terminate and goto failed_removal? Or should we allow a certain number of retrys before we give up on migrating the range?
This issue was observed on a ppc64le lpar on a 4.18-rc6 kernel.
-John
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