On Mon, Apr 14, 2014 at 09:11:25AM +0100, Glyn Normington wrote: > Johannes/Michal > > What are your thoughts on this matter? Do you see this as a valid > requirement? As Tejun said, memory cgroups *do* respond to internal pressure and enter targetted reclaim before invoking the OOM killer. So I'm not exactly sure what you are asking. > On 02/04/2014 19:00, Tejun Heo wrote: > >(cc'ing memcg maintainers and cgroup ML) > > > >On Wed, Apr 02, 2014 at 02:08:04PM +0100, Glyn Normington wrote: > >>Currently, a memory cgroup can hit its oom limit when pages could, in > >>principle, be reclaimed by the kernel except that the kernel does not > >>respond directly to cgroup-local memory pressure. > >So, ummm, it does. > > > >>A use case where this is important is running a moderately large Java > >>application in a memory cgroup in a PaaS environment where cost to the > >>user depends on the memory limit ([1]). Users need to tune the memory > >>limit to reduce their costs. During application initialisation large > >>numbers of JAR files are opened (read-only) and read while loading the > >>application code and its dependencies. This is reflected in a peak of > >>file cache usage which can push the memory cgroup memory usage > >>significantly higher than the value actually needed to run the application. > >> > >>Possible approaches include (1) automatic response to cgroup-local > >>memory pressure in the kernel, and (2) a kernel API for reclaiming > >>memory from a cgroup which could be driven under oom notification (with > >>the oom killer disabled for the cgroup - it would be enabled if the > >>cgroup was still oom after calling the kernel to reclaim memory). > >> > >>Clearly (1) is the preferred approach. The closest facility in the > >>kernel to (2) is to ask the kernel to free pagecache using `echo 1 > > >>/proc/sys/vms/drop_caches`, but that is too wide-ranging, especially in > >>a PaaS environment hosting multiple applications. A similar facility > >>could be provided for a cgroup via a cgroup pseudo-file > >>`memory.drop_caches`. > >> > >>Other approaches include a mempressure cgroup ([2]) which would not be > >>suitable for PaaS applications. See [3] for Andrew Morton's response. A > >>related workaround ([4]) was included in the 3.6 kernel. > >> > >>Related discussions: > >>[1] https://groups.google.com/a/cloudfoundry.org/d/topic/vcap-dev/6M8BDV_tq7w/discussion > >>[2]https://lwn.net/Articles/531077/ <https://lwn.net/Articles/531077/> > >>[3]https://lwn.net/Articles/531138/ <https://lwn.net/Articles/531138/> > >>[4]https://lkml.org/lkml/2013/6/6/462 <https://lkml.org/lkml/2013/6/6/462>& > >>https://github.com/torvalds/linux/commit/e62e384e > >><https://github.com/torvalds/linux/commit/e62e384e>. > -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
