Fix free memory calculation.

base/sys_info_linux.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/sys_info.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <limits>
 
 #include "base/files/file_util.h"
 #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"
 
 namespace {
 
 int64_t AmountOfMemory(int pages_name) {
   long pages = sysconf(pages_name);
   long page_size = sysconf(_SC_PAGESIZE);
   if (pages == -1 || page_size == -1) {
     NOTREACHED();
     return 0;
   }
   return static_cast<int64_t>(pages) * page_size;
 }
 
 int64_t AmountOfPhysicalMemory() {
   return AmountOfMemory(_SC_PHYS_PAGES);
 }
 
 base::LazyInstance<
     base::internal::LazySysInfoValue<int64_t, AmountOfPhysicalMemory>>::Leaky
     g_lazy_physical_memory = LAZY_INSTANCE_INITIALIZER;
 
 }  // namespace
 
 namespace base {
 
 // static
-int64_t SysInfo::AmountOfAvailablePhysicalMemory() {
-  return AmountOfMemory(_SC_AVPHYS_PAGES);
-}
-
-// static
 int64_t SysInfo::AmountOfPhysicalMemory() {
   return g_lazy_physical_memory.Get().value();
 }
 
 // static
+int64_t SysInfo::AmountOfAvailablePhysicalMemory() {
+  SystemMemoryInfoKB info;
+  if (!GetSystemMemoryInfo(&info))
+    return 0;
+  return AmountOfAvailablePhysicalMemory(info);
+}
+
+// static
+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
 std::string SysInfo::CPUModelName() {
 #if defined(OS_CHROMEOS) && defined(ARCH_CPU_ARMEL)
   const char kCpuModelPrefix[] = "Hardware";
 #else
   const char kCpuModelPrefix[] = "model name";
 #endif
   std::string contents;
   ReadFileToString(FilePath("/proc/cpuinfo"), &contents);
   DCHECK(!contents.empty());
   if (!contents.empty()) {
     std::istringstream iss(contents);
     std::string line;
     while (std::getline(iss, line)) {
       if (line.compare(0, strlen(kCpuModelPrefix), kCpuModelPrefix) == 0) {
         size_t pos = line.find(": ");
         return line.substr(pos + 2);
       }
     }
   }
   return std::string();
 }
 
 }  // namespace base