On Tue, Dec 19, 2017 at 4:49 AM, Michal Hocko <mhocko@xxxxxxxxxx> wrote: > On Mon 18-12-17 16:01:31, Shakeel Butt wrote: >> The memory controller in cgroup v1 provides the memory+swap (memsw) >> interface to account to the combined usage of memory and swap of the >> jobs. The memsw interface allows the users to limit or view the >> consistent memory usage of their jobs irrespectibe of the presense of >> swap on the system (consistent OOM and memory reclaim behavior). The >> memory+swap accounting makes the job easier for centralized systems >> doing resource usage monitoring, prediction or anomaly detection. >> >> In cgroup v2, the 'memsw' interface was dropped and a new 'swap' >> interface has been introduced which allows to limit the actual usage of >> swap by the job. For the systems where swap is a limited resource, >> 'swap' interface can be used to fairly distribute the swap resource >> between different jobs. There is no easy way to limit the swap usage >> using the 'memsw' interface. >> >> However for the systems where the swap is cheap and can be increased >> dynamically (like remote swap and swap on zram), the 'memsw' interface >> is much more appropriate as it makes swap transparent to the jobs and >> gives consistent memory usage history to centralized monitoring systems. >> >> This patch adds memsw interface to cgroup v2 memory controller behind a >> mount option 'memsw'. The memsw interface is mutually exclusive with >> the existing swap interface. When 'memsw' is enabled, reading or writing >> to 'swap' interface files will return -ENOTSUPP and vice versa. Enabling >> or disabling memsw through remounting cgroup v2, will only be effective >> if there are no decendants of the root cgroup. >> >> When memsw accounting is enabled then "memory.high" is comapred with >> memory+swap usage. So, when the allocating job's memsw usage hits its >> high mark, the job will be throttled by triggering memory reclaim. > > From a quick look, this looks like a mess. The main motivation behind this patch is to convince that memsw has genuine use-cases. How to provide memsw is still in RFC stage. Suggestions and comments are welcomed. > We have agreed to go with > the current scheme for some good reasons. Yes I agree, when the swap is a limited resource the current 'swap' interface should be used to fairly distribute it between different jobs. > There are cons/pros for both > approaches but I am not convinced we should convolute the user API for > the usecase you describe. > Yes, there are pros & cons, therefore we should give users the option to select the API that is better suited for their use-cases and environment. Both approaches are not interchangeable. We use memsw internally for use-cases I mentioned in commit message. This is one of the main blockers for us to even consider cgroup-v2 for memory controller. >> Signed-off-by: Shakeel Butt <shakeelb@xxxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
