ping On Sun, Sep 21, 2014 at 07:14:32PM +0400, Vladimir Davydov wrote: > Hi, > > Kmem accounting of memcg is unusable now, because it lacks slab shrinker > support. That means when we hit the limit we will get ENOMEM w/o any > chance to recover. What we should do then is to call shrink_slab, which > would reclaim old inode/dentry caches from this cgroup. This is what > this patch set is intended to do. > > Basically, it does two things. First, it introduces the notion of > per-memcg slab shrinker. A shrinker that wants to reclaim objects per > cgroup should mark itself as SHRINKER_MEMCG_AWARE. Then it will be > passed the memory cgroup to scan from in shrink_control->memcg. For such > shrinkers shrink_slab iterates over the whole cgroup subtree under the > target cgroup and calls the shrinker for each kmem-active memory cgroup. > > Secondly, this patch set makes the list_lru structure per-memcg. It's > done transparently to list_lru users - everything they have to do is to > tell list_lru_init that they want memcg-aware list_lru. Then the > list_lru will automatically distribute objects among per-memcg lists > basing on which cgroup the object is accounted to. This way to make FS > shrinkers (icache, dcache) memcg-aware we only need to make them use > memcg-aware list_lru, and this is what this patch set does. > > The main difference of this patch set from my previous attempts to push > memcg aware shrinkers is in how it handles css offline. Now we don't let > list_lrus corresponding to dead memory cgroups hang around till all > objects are freed. Instead we move lru items to the parent cgroup's lru > list. This is really important, because this allows us to release > memcg_cache_id used for indexing in per-memcg arrays. If we don't do > this, the arrays will grow uncontrollably, which is really bad. Note, in > comparison to user memory reparenting, which Johannes is going to get > rid of, it's not racy and much easier to implement although it does > impose some limitations on how list_lru locking can be implemented. > Another difference is that it doesn't reparent charges, only list_lru > entries - the css will be dangling until the last kmem object is freed. > > As before, this patch set only enables per-memcg kmem reclaim when the > pressure goes from memory.limit, not from memory.kmem.limit. Handling > memory.kmem.limit is going to be tricky due to GFP_NOFS allocations, it > will probably require a sort of soft limit to work properly. I'm leaving > this for future work. > > The patch set basically consists of three main parts and organized as > follows: > > - Patches 1-3 implement per-memcg shrinker core with patches 1 and 2 > preparing list_lru users for upcoming changes and patch 3 tuning > shrink_slab. > > - Patches 4-10 make memcg core release cache ids on offline doing a bit > of cleanup in the meanwhile. This is easy, because kmem_caches don't > need the cache id after css offline since there can't be allocations > going from a dead memcg. Note that most of these patches (namely 4-6, > and 8) were once merged, but then I decided to drop them, because I > didn't know how to deal with list_lrus at that time (see > https://lkml.org/lkml/2014/7/23/218). > > - Finally patches 11-14 make list_lru per-memcg and mark FS shrinkers > as memcg-aware. This is the most difficult part of this patch set > with patch 13 (unlucky :-) doing the most important work. > > Reviews are more than welcome. -- 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>