Hi Greg, On Wed, Sep 17, 2014 at 09:04:00PM -0700, Greg Thelen wrote: > I've found per memcg per cache type stats useful in answering "why is my > container oom?" While these are kernel allocations, it is common for > user space operations to cause these allocations (e.g. lots of open file > descriptors). So I don't specifically need per memcg slabinfo formatted > data, but at the least a per memcg per cache type active object count > would be very useful. Thus I imagine each memcg would have an array of > slab cache types each with per-cpu active object counters. Per-cpu is > used to avoid trashing those counters between cpus as objects are > allocated and freed. Hmm, that sounds sane. One more argument for the current design. > As you say only memcg shrinkable cache types would need list heads. I > assume these per memcg shrinkable object list heads would be per cache > type per cpu list heads for cache performance. Allocation of a dentry > today uses the normal slab management structures. In this proposal I > suspect the dentry would be dual indexed: once in the global slab/slub > dentry lru and once in the per memcg dentry list. If true, this might > be a hot path regression allocation speed regression. > > Do you have a shrinker design in mind? I suspect this new design would > involve a per memcg dcache shrinker which grabs a big per-memcg dcache > lock while walking the dentry list. The classic per superblock > shrinkers would not used for memcg shrinking. To be honest, I hadn't elaborated that in my mind when I sent this e-mail, but now I realize that it doesn't look as if there's an easy way to implement shrinkers in such a setup efficiently. I thought we could keep each dentry/inode simultaneously in two list, global and memcg. However, apart from resulting in memory wastes this, as you pointed out, would result in a regression in operating on the lrus, which is unacceptable. That said, I admit my idea sounds crazy. I think sticking to Glauber's design and trying to make it work is the best we can do now. Thanks, Vladimir -- 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>