On Tue, May 28, 2019 at 09:33:02PM +0300, Vladimir Davydov wrote: > 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. Hi Vladimir! Thank you for looking into the series. Really appreciate it! It looks like outstanding questions are: 1) synchronization around the dying flag 2) removing CONFIG_SLOB in 2/7 3) early sysfs_slab_remove() 4) mem_cgroup_from_kmem in 7/7 Please, let me know if I missed anything. I'm waiting now for Johanness's review, so I'll address these issues in background and post the next (and hopefully) final version. Thanks!
