On Mon 08-10-12 14:06:20, Glauber Costa wrote: > Signed-off-by: Glauber Costa <glommer@xxxxxxxxxxxxx> > --- > Documentation/cgroups/memory.txt | 55 +++++++++++++++++++++++++++++++++++++++- > 1 file changed, 54 insertions(+), 1 deletion(-) > > diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt > index c07f7b4..9b08548 100644 > --- a/Documentation/cgroups/memory.txt > +++ b/Documentation/cgroups/memory.txt > @@ -71,6 +71,11 @@ Brief summary of control files. > memory.oom_control # set/show oom controls. > memory.numa_stat # show the number of memory usage per numa node > > + memory.kmem.limit_in_bytes # set/show hard limit for kernel memory > + memory.kmem.usage_in_bytes # show current kernel memory allocation > + memory.kmem.failcnt # show the number of kernel memory usage hits limits > + memory.kmem.max_usage_in_bytes # show max kernel memory usage recorded > + > memory.kmem.tcp.limit_in_bytes # set/show hard limit for tcp buf memory > memory.kmem.tcp.usage_in_bytes # show current tcp buf memory allocation > memory.kmem.tcp.failcnt # show the number of tcp buf memory usage hits limits > @@ -268,20 +273,62 @@ the amount of kernel memory used by the system. Kernel memory is fundamentally > different than user memory, since it can't be swapped out, which makes it > possible to DoS the system by consuming too much of this precious resource. > > +Kernel memory won't be accounted at all until it is limited. This allows for until limit on a group is set. > +existing setups to continue working without disruption. Note that it is > +possible to account it without an effective limit by setting the limits > +to a very high number (like RESOURCE_MAX -1page). I have brought that up in an earlier patch already. Why not just do echo -1 (which translates to RESOURCE_MAX internally) and be done with that. RESOURCE_MAX-1 sounds quite inconvenient. > The limit cannot be set > +if the cgroup have children, or if there are already tasks in the cgroup. I would start by stating that if children are accounted automatically if their parent is accounted already and there is no need to set a limit to enforce that. In fact the limit cannot be set if .... > + > +After a controller is first limited, it will be kept being accounted until it group is limited not the controller. > +is removed. The memory limitation itself, can of course be removed by writing > +-1 to memory.kmem.limit_in_bytes This might be confusing and one could think that also accounting would be removed. I wouldn't mention it at all. > + > Kernel memory limits are not imposed for the root cgroup. Usage for the root > -cgroup may or may not be accounted. > +cgroup may or may not be accounted. The memory used is accumulated into > +memory.kmem.usage_in_bytes, or in a separate counter when it makes sense. Which separate counter? Is this about tcp kmem? > +The main "kmem" counter is fed into the main counter, so kmem charges will > +also be visible from the user counter. > > Currently no soft limit is implemented for kernel memory. It is future work > to trigger slab reclaim when those limits are reached. > > 2.7.1 Current Kernel Memory resources accounted > > +* stack pages: every process consumes some stack pages. By accounting into > +kernel memory, we prevent new processes from being created when the kernel > +memory usage is too high. > + > * sockets memory pressure: some sockets protocols have memory pressure > thresholds. The Memory Controller allows them to be controlled individually > per cgroup, instead of globally. > > * tcp memory pressure: sockets memory pressure for the tcp protocol. > > +2.7.3 Common use cases > + > +Because the "kmem" counter is fed to the main user counter, kernel memory can > +never be limited completely independently of user memory. Say "U" is the user > +limit, and "K" the kernel limit. There are three possible ways limits can be > +set: > + > + U != 0, K = 0: K is not 0 it is unaccounted (disabled) > + This is the standard memcg limitation mechanism already present before kmem > + accounting. Kernel memory is completely ignored. > + > + U,K != 0, K < U: I would keep K < U > + Kernel memory is effectively set as a percentage of the user memory. This not a percentage it is subset of the user memory > + setup is useful in deployments where the total amount of memory per-cgroup > + is overcommited. Overcommiting kernel memory limits is definitely not > + recommended, since the box can still run out of non-reclaimable memory. > + In this case, the admin could set up K so that the sum of all groups is > + never greater than the total memory, and freely set U at the cost of his > + QoS. > + > + U,K != 0, K >= U: > + Since kmem charges will also be fed to the user counter, this setup gives > + the admin a unified view of memory. Reclaim will be triggered for the cgroup > + for both kinds of memory. This is also useful for tracking kernel memory allocation. > + > 3. User Interface > > 0. Configuration > @@ -290,6 +337,7 @@ a. Enable CONFIG_CGROUPS > b. Enable CONFIG_RESOURCE_COUNTERS > c. Enable CONFIG_MEMCG > d. Enable CONFIG_MEMCG_SWAP (to use swap extension) > +d. Enable CONFIG_MEMCG_KMEM (to use kmem extension) > > 1. Prepare the cgroups (see cgroups.txt, Why are cgroups needed?) > # mount -t tmpfs none /sys/fs/cgroup > @@ -406,6 +454,11 @@ About use_hierarchy, see Section 6. > Because rmdir() moves all pages to parent, some out-of-use page caches can be > moved to the parent. If you want to avoid that, force_empty will be useful. > > + Also, note that when memory.kmem.limit_in_bytes is set the charges due to > + kernel pages will still be seen. This is not considered a failure and the > + write will still return success. In this case, it is expected that > + memory.kmem.usage_in_bytes == memory.usage_in_bytes. > + > About use_hierarchy, see Section 6. > > 5.2 stat file > -- > 1.7.11.4 > > -- > 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 -- 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>