Fix free memory calculation.

base/sys_info_linux.cc

Index: base/sys_info_linux.cc
diff --git a/base/sys_info_linux.cc b/base/sys_info_linux.cc
index 298d245ecf580da4d8790f5dc47f851c0208ab5d..0cd05b363a23e34ae270ececb8c995305cd3eded 100644
--- a/base/sys_info_linux.cc
+++ b/base/sys_info_linux.cc
@@ -13,6 +13,7 @@
 #include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/numerics/safe_conversions.h"
+#include "base/process/process_metrics.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/sys_info_internal.h"
 #include "build/build_config.h"
@@ -42,13 +43,29 @@ base::LazyInstance<
 namespace base {
 
 // static
+int64_t SysInfo::AmountOfPhysicalMemory() {
+  return g_lazy_physical_memory.Get().value();
+}
+
+// static
 int64_t SysInfo::AmountOfAvailablePhysicalMemory() {
-  return AmountOfMemory(_SC_AVPHYS_PAGES);
+  SystemMemoryInfoKB info;
+  if (!GetSystemMemoryInfo(&info))
+    return 0;
+  return AmountOfAvailablePhysicalMemory(info);
 }
 
 // static
-int64_t SysInfo::AmountOfPhysicalMemory() {
-  return g_lazy_physical_memory.Get().value();
+int64_t SysInfo::AmountOfAvailablePhysicalMemory(
+    const SystemMemoryInfoKB& info) {
+  // See details here:
+  // https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=34e431b0ae398fc54ea69ff85ec700722c9da773
+  // The fallback logic (when there is no MemAvailable) would be more precise
+  // if we had info about zones watermarks (/proc/zoneinfo).
+  int64_t res_kb = info.available != 0
+                       ? info.available - info.active_file
+                       : info.free + info.reclaimable + info.inactive_file;
+  return res_kb * 1024;
 }
 
 // static