On Tue, May 28, 2019 at 07:58:17PM +0000, Roman Gushchin wrote: > 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. The todo items here aside, the series looks good to me - although I'm glad that Vladimir gave it a much more informed review than I could.
