On Tue, 12 Oct 2010 00:32:33 -0700 Greg Thelen <gthelen@xxxxxxxxxx> wrote: > KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> writes: > >> What are the cases where current->mm->owner->cgroups != > >> current->cgroups? > >> > > In that case, assume group A and B. > > > > thread(1) -> belongs to cgroup A (thread(1) is mm->owner) > > thread(2) -> belongs to cgroup B > > and > > a page -> charnged to cgroup A > > > > Then, thread(2) make the page dirty which is under cgroup A. > > > > In this case, if page's dirty_pages accounting is added to cgroup B, > > cgroup B' statistics may show "dirty_pages > all_lru_pages". This is > > bug. > > I agree that in this case the dirty_pages accounting should be added to > cgroup A because that is where the page was charged. This will happen > because pc->mem_cgroup was set to A when the page was charged. The > mark-page-dirty code will check pc->mem_cgroup to determine which cgroup > to add the dirty page to. > > I think that the current vs current->mm->owner decision is in areas of > the code that is used to query the dirty limits. These routines do not > use this data to determine which cgroup to charge for dirty pages. The > usage of either mem_cgroup_from_task(current->mm->owner) or > mem_cgroup_from_task(current) in mem_cgroup_has_dirty_limit() does not > determine which cgroup is added for dirty_pages. > mem_cgroup_has_dirty_limit() is only used to determine if the process > has a dirty limit. As discussed, this is a momentary answer that may be > wrong by the time decisions are made because the task may be migrated > in-to/out-of root cgroup while mem_cgroup_has_dirty_limit() runs. If > the process has a dirty limit, then the process's memcg is used to > compute dirty limits. Using your example, I assume that thread(1) and > thread(2) will git dirty limits from cgroup(A) and cgroup(B) > respectively. > Ok, thank you for clarification. Throttoling a thread based on its own cgroup not based on mm->owner makes sense. Could you add a brief comment on the code ? Thanks, -Kame -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>