On 01/26/2013 03:59 AM, Andrew Morton wrote: > On Tue, 22 Jan 2013 17:47:38 +0400 > Glauber Costa <glommer@xxxxxxxxxxxxx> wrote: > >> Currently, we use cgroups' provided list of children to verify if it is >> safe to proceed with any value change that is dependent on the cgroup >> being empty. >> >> This is less than ideal, because it enforces a dependency over cgroup >> core that we would be better off without. The solution proposed here is >> to iterate over the child cgroups and if any is found that is already >> online, we bounce and return: we don't really care how many children we >> have, only if we have any. >> >> This is also made to be hierarchy aware. IOW, cgroups with hierarchy >> disabled, while they still exist, will be considered for the purpose of >> this interface as having no children. > > The code comments are a bit unclear. Did this improve them? Both versions seem clear to me, so I'll go with yours as a tie breaker =p One thing to keep in mind: > - * must be called with cgroup_lock held, unless the cgroup is guaranteed to be > - * already dead (like in mem_cgroup_force_empty, for instance). This is > - * different than mem_cgroup_count_children, in the sense that we don't really > - * care how many children we have, we only need to know if we have any. It is > - * also count any memcg without hierarchy as infertile for that matter. > + * Must be called with cgroup_lock held, unless the cgroup is guaranteed to be > + * already dead (in mem_cgroup_force_empty(), for instance). This is different > + * from mem_cgroup_count_children(), in the sense that we don't really care how > + * many children we have; we only need to know if we have any. It also counts > + * any memcg without hierarchy as infertile. > */ In a later patch, I update this text to reflect the fact that the memcg_mutex will now play this role instead of the cgroup_lock. So I am just mentioning the cgroup lock here for temporary consistency. We need to make sure that the later patch still applies, or we'll be left with a bogus comment. -- 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>