On Wed 04-07-12 15:13:02, Johannes Weiner wrote: > On Wed, Jul 04, 2012 at 02:04:45PM +0200, Michal Hocko wrote: > > On Wed 04-07-12 10:30:19, Johannes Weiner wrote: [...] > > > Can we instead not charge the new page, just commit it while holding > > > on to a css refcount, and have end_migration call a version of > > > __mem_cgroup_uncharge_common() that updates the stats but leaves the > > > res counters alone? > > > > Yes, this is also a way to go. Both approaches have to lie a bit and > > both have a discrepancy between stat and usage_in_bytes. I guess we can > > live with that. > > Kame's solution seems easier but yours prevent from a corner case when > > the reclaim is triggered due to artificial charges so I guess it is > > better to go with yours. > > Few (trivial) comments on the patch bellow. > > It's true that the cache/rss statistics still account for both pages. > But they don't have behavioural impact and so I didn't bother. Only if somebody watches those numbers and blows up if rss+cache > limit_in_bytes. I can imagine an LTP test like that. But the test would need to trigger migration in the background... > We could still fix this up later, but it's less urgent, I think. Yes, I guess so > > > > @@ -2955,7 +2956,10 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype) > > > /* fallthrough */ > > > case MEM_CGROUP_CHARGE_TYPE_DROP: > > > /* See mem_cgroup_prepare_migration() */ > > > - if (page_mapped(page) || PageCgroupMigration(pc)) > > > + if (page_mapped(page)) > > > + goto unlock_out; > > > > Don't need that test or remove the one below (seems easier to read > > because those cases are really different things). > > > > > + if (page_mapped(page) || (!end_migration && > > > + PageCgroupMigration(pc))) > > My bad, I meant to remove this second page_mapped() and forgot. Will > fix. I take it > > if (page_mapped(page)) > goto unlock_out; > if (!end_migration && PageCgroupMigration(pc)) > goto unlock_out; > > is what you had in mind? Yes -- Michal Hocko SUSE Labs SUSE LINUX s.r.o. Lihovarska 1060/12 190 00 Praha 9 Czech Republic -- 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>