On Tue 27-10-15 09:42:27, Johannes Weiner wrote: > On Tue, Oct 27, 2015 at 05:15:54PM +0100, Michal Hocko wrote: > > On Tue 27-10-15 11:41:38, Johannes Weiner wrote: [...] > Or it could be exactly the other way around when you have a workload > that is heavy on filesystem metadata. I don't see why any scenario > would be more important than the other. Yes I definitely agree. No scenario is more important. We can only come up with a default that makes more sense for the majority and allow the minority to override. That was what I wanted to say basically. > I'm not saying that distinguishing between consumers is wrong, just > that "user memory vs kernel memory" is a false classification. Why do > you call page cache user memory but dentry cache kernel memory? It > doesn't make any sense. We are not talking about dcache vs. page cache alone here, though. We are talking about _all_ slab allocations vs. only user accessed memory. The slab consumption is directly under kernel control. A great pile of this logic is completly hidden from userspace. While user can estimate the user memory it is hard (if possible) to do that for the kernel memory footprint - not even mentioning this is variable and dependent on the particular kernel version. > > Also kmem accounting will make the load more non-deterministic because > > many of the resources are shared between tasks in separate cgroups > > unless they are explicitly configured. E.g. [id]cache will be shared > > and first to touch gets charged so you would end up with more false > > sharing. > > Exactly like page cache. This differentiation isn't based on reality. Yes false sharing is an existing and long term problem already. I just wanted to point out that the false sharing would be even a bigger problem because some kernel tracked resources are shared more naturally than file sharing. > > > IMO that's an implementation detail and a historical artifact that > > > should not be exposed to the user. And that's the thing I hate about > > > the current opt-out knob. > > You carefully skipped over this part. We can ignore it for socket > memory but it's something we need to figure out when it comes to slab > accounting and tracking. I am sorry, I didn't mean to skip this part, I though it would be clear from the previous text. I think kmem accounting falls into the same category. Have a sane default and a global boottime knob to override it for those that think differently - for whatever reason they might have. [...] > Having page cache accounting built in while presenting dentry+inode > cache as a configurable extension is completely random and doesn't > make sense. They are both first class memory consumers. They're not > separate categories. One isn't more "core" than the other. Again we are talking about all slab allocations not just the dcache. > > > For now, something like this as a boot commandline? > > > > > > cgroup.memory=nosocket > > > > That would work for me. > > Okay, then I'll go that route for the socket stuff. Thanks! -- Michal Hocko SUSE Labs -- 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>