Report total memory based on limit or host

gVisor was previously reporting the lower of cgroup limit or 2GB as total
memory. This may cause applications to make bad decisions based on amount
of memory available to them when more than 2GB is required.

This change makes the lower of cgroup limit or the host total memory to be
reported inside the sandbox. This also is more inline with docker which always
reports host total memory. Note that reporting cgroup limit is strictly better
than host total memory when there is a limit set.

Fixes #5608

PiperOrigin-RevId: 403241608

1 files changed, 70 insertions, 0 deletions

diff --git a/runsc/sandbox/memory.go b/runsc/sandbox/memory.go
new file mode 100644
index 000000000..77b88eb89
--- /dev/null
+++ b/runsc/sandbox/memory.go
@@ -0,0 +1,70 @@
+// Copyright 2021 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package sandbox
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"os"
+	"strconv"
+	"strings"
+)
+
+// totalSystemMemory extracts "MemTotal" from "/proc/meminfo".
+func totalSystemMemory() (uint64, error) {
+	f, err := os.Open("/proc/meminfo")
+	if err != nil {
+		return 0, err
+	}
+	defer f.Close()
+	return parseTotalSystemMemory(f)
+}
+
+func parseTotalSystemMemory(r io.Reader) (uint64, error) {
+	for scanner := bufio.NewScanner(r); scanner.Scan(); {
+		line := scanner.Text()
+		totalStr := strings.TrimPrefix(line, "MemTotal:")
+		if len(totalStr) < len(line) {
+			fields := strings.Fields(totalStr)
+			if len(fields) == 0 || len(fields) > 2 {
+				return 0, fmt.Errorf(`malformed "MemTotal": %q`, line)
+			}
+			totalStr = fields[0]
+			unit := ""
+			if len(fields) == 2 {
+				unit = fields[1]
+			}
+			mem, err := strconv.ParseUint(totalStr, 10, 64)
+			if err != nil {
+				return 0, err
+			}
+			switch unit {
+			case "":
+				// do nothing.
+			case "kB":
+				memKb := mem
+				mem = memKb * 1024
+				if mem < memKb {
+					return 0, fmt.Errorf(`"MemTotal" too large: %d`, memKb)
+				}
+			default:
+				return 0, fmt.Errorf("unknown unit %q: %q", unit, line)
+			}
+			return mem, nil
+		}
+	}
+	return 0, fmt.Errorf(`malformed "/proc/meminfo": "MemTotal" not found`)
+}