Extend class comments.

2 files changed, 27 insertions, 2 deletions

diff --git a/vespalib/src/vespa/vespalib/util/cgroup_resource_limits.h b/vespalib/src/vespa/vespalib/util/cgroup_resource_limits.h
index 04fc0384c1a..72333195545 100644
--- a/vespalib/src/vespa/vespalib/util/cgroup_resource_limits.h
+++ b/vespalib/src/vespa/vespalib/util/cgroup_resource_limits.h
@@ -11,7 +11,28 @@
 namespace vespalib {
 
 /*
- * Class for getting cgroup resource limits.
+ * Class for getting cgroup resource limits (memory and cpu resources).
+ *
+ * Cgroups version 1 and version 2 are handled, but a mix of cgroups version 1
+ * and cgroups version 2 is not handled.
+ *
+ * Systemd resource control unit settings applied to cgroups (cf.
+ * systemd.resource-control(5) manual page on Linux) and
+ * container resource limit (set by e.g. docker and podman) applied to cgroups
+ * should be reflected in the sampled resource limits.
+ *
+ * The --cpus and --memory options for docker/podman create are reflected
+ * in cgroup limits that are sampled, but the cgroup limit affected by the
+ * --cpuset-cpus option is not yet sampled.
+ *
+ * For cgroups version 1, "memory.limit_in_bytes", "cpu.cfs_quota_us" and
+ * "cpu.cfs_period_us" are sampled.
+ *
+ * For cgroups version 2, "memory.max" and "cpu.max" are sampled.
+ *
+ * This is intended to be used by vespa-proton-bin running on the host
+ * or in a container, as a systemd service or not, with cgroups
+ * version 1 or cgroups version 2.
  */
 class CGroupResourceLimits {
     std::optional<uint64_t> _memory_limit;
diff --git a/vespalib/src/vespa/vespalib/util/resource_limits.h b/vespalib/src/vespa/vespalib/util/resource_limits.h
index 7255cef9df5..8e1c7a7c34f 100644
--- a/vespalib/src/vespa/vespalib/util/resource_limits.h
+++ b/vespalib/src/vespa/vespalib/util/resource_limits.h
@@ -7,7 +7,11 @@
 namespace vespalib {
 
 /*
- * Class for getting resource limits.
+ * Class for getting resource limits. Memory limit is first sampled by
+ * using sysconf to get page size and number of physical pages.
+ * Cpu limit is first sampled by calling std::thread::hardware_concurrency().
+ * Both limits can be adjusted downwards by applying some of the cgroup limits
+ * for the current process, cf. CGroupResourceLimits).
  */
 class ResourceLimits {
     uint64_t _memory;