(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>. -- tejun -- 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
