On Tue, May 21, 2019 at 01:07:34PM -0700, Roman Gushchin wrote: > Let's reparent memcg slab memory on memcg offlining. This allows us > to release the memory cgroup without waiting for the last outstanding > kernel object (e.g. dentry used by another application). > > So instead of reparenting all accounted slab pages, let's do reparent > a relatively small amount of kmem_caches. Reparenting is performed as > a part of the deactivation process. > > Since the parent cgroup is already charged, everything we need to do > is to splice the list of kmem_caches to the parent's kmem_caches list, > swap the memcg pointer and drop the css refcounter for each kmem_cache > and adjust the parent's css refcounter. Quite simple. > > Please, note that kmem_cache->memcg_params.memcg isn't a stable > pointer anymore. It's safe to read it under rcu_read_lock() or > with slab_mutex held. > > We can race with the slab allocation and deallocation paths. It's not > a big problem: parent's charge and slab global stats are always > correct, and we don't care anymore about the child usage and global > stats. The child cgroup is already offline, so we don't use or show it > anywhere. > > Local slab stats (NR_SLAB_RECLAIMABLE and NR_SLAB_UNRECLAIMABLE) > aren't used anywhere except count_shadow_nodes(). But even there it > won't break anything: after reparenting "nodes" will be 0 on child > level (because we're already reparenting shrinker lists), and on > parent level page stats always were 0, and this patch won't change > anything. > > Signed-off-by: Roman Gushchin <guro@xxxxxx> > Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx> This one looks good to me. I can't see why anything could possibly go wrong after this change.
