On Fri, Jun 06 2014, Michal Hocko <mhocko@xxxxxxx> wrote: > Some users (e.g. Google) would like to have stronger semantic than low > limit offers currently. The fallback mode is not desirable and they > prefer hitting OOM killer rather than ignoring low limit for protected > groups. There are other possible usecases which can benefit from hard > guarantees. I can imagine workloads where setting low_limit to the same > value as hard_limit to prevent from any reclaim at all makes a lot of > sense because reclaim is much more disrupting than restart of the load. > > This patch adds a new per memcg memory.reclaim_strategy knob which > tells what to do in a situation when memory reclaim cannot do any > progress because all groups in the reclaimed hierarchy are within their > low_limit. There are two options available: > - low_limit_best_effort - the current mode when reclaim falls > back to the even reclaim of all groups in the reclaimed > hierarchy > - low_limit_guarantee - groups within low_limit are never > reclaimed and OOM killer is triggered instead. OOM message > will mention the fact that the OOM was triggered due to > low_limit reclaim protection. To (a) be consistent with existing hard and soft limits APIs and (b) allow use of both best effort and guarantee memory limits, I wonder if it's best to offer three per memcg limits, rather than two limits (hard, low_limit) and a related reclaim_strategy knob. The three limits I'm thinking about are: 1) hard_limit (aka the existing limit_in_bytes cgroupfs file). No change needed here. This is an upper bound on a memcg hierarchy's memory consumption (assuming use_hierarchy=1). 2) best_effort_limit (aka desired working set). This allow an application or administrator to provide a hint to the kernel about desired working set size. Before oom'ing the kernel is allowed to reclaim below this limit. I think the current soft_limit_in_bytes claims to provide this. If we prefer to deprecate soft_limit_in_bytes, then a new desired_working_set_in_bytes (or a hopefully better named) API seems reasonable. 3) low_limit_guarantee which is a lower bound of memory usage. A memcg would prefer to be oom killed rather than operate below this threshold. Default value is zero to preserve compatibility with existing apps. Logically hard_limit >= best_effort_limit >= low_limit_guarantee. -- 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>