Resurrect v1

base/base/getMemoryAmount.cpp

@@ -77,10 +77,25 @@ uint64_t getMemoryAmountOrZero()
     uint64_t memory_amount = num_pages * page_size;
 
     /// Respect the memory limit set by cgroups v2.
-    /// Cgroups v1 is dead since many years and its limits are not considered for simplicity.
     auto limit = getCgroupsV2MemoryLimit("memory.max");
+
     if (limit.has_value() && *limit < memory_amount)
          memory_amount = *limit;
+    else
+    {
+        /// Cgroups v1 were replaced by v2 in 2015. The only reason we keep supporting v1 is that the transition to v2
+        /// has been slow. Caveat : Hierarchical groups as in v2 are not supported for v1, the location of the memory
+        /// limit (virtual) file is hard-coded.
+        /// TODO: check at the end of 2024 if we can get rid of v1.
+        std::ifstream cgroup_limit("/sys/fs/cgroup/memory/memory.limit_in_bytes");
+        if (cgroup_limit.is_open())
+        {
+            uint64_t memory_limit = 0; // in case of read error
+            cgroup_limit >> memory_limit;
+            if (memory_limit > 0 && memory_limit < memory_amount)
+                memory_amount = memory_limit;
+        }
+    }
 
     return memory_amount;
 }