On Wed, 3 Feb 2016, Johannes Weiner wrote: > CCing Hugh and Greg, they have worked on the memcg migration code most > recently. AFAIK the only reason newpage->mem_cgroup had to be set up > that early in migration was because of the way dirty accounting used > to work. But Hugh took memcg out of the equation there, so moving > mem_cgroup_migrate() to the end should be safe, as long as the pages > are still locked and off the LRU. Yes, that should be safe now: Vladimir's patch looks okay to me, fixing the immediate irq issue. But it would be nicer, if mem_cgroup_migrate() were called solely from migrate_page_copy() - deleting the other calls in mm/migrate.c, including that from migrate_misplaced_transhuge_page() (which does some rewinding on error after its migrate_page_copy(): but just as you now let a successfully migrated old page be uncharged when it's freed, so you can leave a failed new_page to be uncharged when it's freed, no extra code needed). And (even more off-topic), I'm slightly sad to see that the lrucare arg which mem_cgroup_migrate() used to have (before I renamed it and you renamed it back!) has gone, so mem_cgroup_migrate() now always demands lrucare of commit_charge(). I'd hoped that with your separation of new from old charge, mem_cgroup_migrate() would never need lrucare; but that's not true for the fuse case, though true for everyone else. Maybe just not worth bothering about? Or the reintroduction of some unnecessary zone->lru_lock-ing in page migration, which we ought to try to avoid? Or am I wrong, and even fuse doesn't need it? That early return "if (newpage->mem_cgroup)": isn't mem_cgroup_migrate() a no-op for fuse, or is there some corner case by which newpage can be on LRU but its mem_cgroup unset? Hugh -- 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>