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
