On Fri, 2 Mar 2012 20:27:53 +0400 Anton Vorontsov <anton.vorontsov@xxxxxxxxxx> wrote: > ... and thus is useless for low memory notifications. > > Hi all! > > While working on userspace low memory killer daemon (a supposed > substitution for the kernel low memory killer, i.e. > drivers/staging/android/lowmemorykiller.c), I noticed that current > cgroups memory notifications aren't suitable for such a daemon. > > Suppose we want to install a notification when free memory drops below > 8 MB. Logically (taking memory hotplug aside), using current usage_in_bytes > notifications we would install an event on 'total_ram - 8MB' threshold. > > But as usage_in_bytes doesn't account file mapped memory and memory > used by kernel slab, the formula won't work. > > Currently I use the following patch that makes things going: > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 228d646..c8abdc5 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -3812,6 +3812,9 @@ static inline u64 mem_cgroup_usage(struct mem_cgroup *memcg, bool swap) > > val = mem_cgroup_recursive_stat(memcg, MEM_CGROUP_STAT_CACHE); > val += mem_cgroup_recursive_stat(memcg, MEM_CGROUP_STAT_RSS); > + val += mem_cgroup_recursive_stat(memcg, MEM_CGROUP_STAT_FILE_MAPPED); > + val += global_page_state(NR_SLAB_RECLAIMABLE); > + val += global_page_state(NR_SLAB_UNRECLAIMABLE); > > > But here are some questions: > > 1. Is there any particular reason we don't currently account file mapped > memory in usage_in_bytes? > CACHE includes all file caches. Why do you think FILE_MAPPED is not included in CACHE ? > To me, MEM_CGROUP_STAT_FILE_MAPPED hunk seems logical even if we > don't use it for lowmemory notifications. > > Plus, it seems that FILE_MAPPED _is_ accounted for the non-root > cgroups, so I guess it's clearly a bug for the root memcg? > > 2. As for NR_SLAB_RECLAIMABLE and NR_SLAB_UNRECLAIMABLE, it seems that > these numbers are only applicable for the root memcg. > I'm not sure that usage_in_bytes semantics should actually account > these, but I tend to think that we should. > Now, SLAB is not accounted by memcg at all. See memifo if necessary. > All in all, not accounting both 1. and 2. looks like bugs to me. > It's spec. not bug. If you want to see slab status in memcg's file, Please add kernel memory accounting feature. There has been already 2 proposals. Check them and comment. Thanks, -Kame -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>