From 19743f3085cc6fc865af33f0aa08d91d64499c0c Mon Sep 17 00:00:00 2001
From: Tudor Brindus <me@tbrindus.ca>
Date: Fri, 20 Mar 2020 17:37:22 -0400
Subject: [PATCH] fix(memory): provide better free memory approximation on old
 kernels

The approximation should include SReclaimable, and subtract Shmem. To
prevent the parsing code from ballooning in size, this commit also
refactors the parsing into a map.
---
 include/modules/memory.hpp |  3 +--
 src/modules/memory.cpp     | 41 ++++++++++++++++++--------------------
 2 files changed, 20 insertions(+), 24 deletions(-)

diff --git a/include/modules/memory.hpp b/include/modules/memory.hpp
index be66611e..5b0f51bb 100644
--- a/include/modules/memory.hpp
+++ b/include/modules/memory.hpp
@@ -17,8 +17,7 @@ class Memory : public ALabel {
   static inline const std::string data_dir_ = "/proc/meminfo";
   void                            parseMeminfo();
 
-  unsigned long memtotal_;
-  unsigned long memfree_;
+  std::unordered_map<std::string, unsigned long> meminfo_;
 
   util::SleeperThread thread_;
 };
diff --git a/src/modules/memory.cpp b/src/modules/memory.cpp
index eeb92bfe..6aa7036c 100644
--- a/src/modules/memory.cpp
+++ b/src/modules/memory.cpp
@@ -10,11 +10,23 @@ waybar::modules::Memory::Memory(const std::string& id, const Json::Value& config
 
 auto waybar::modules::Memory::update() -> void {
   parseMeminfo();
-  if (memtotal_ > 0 && memfree_ >= 0) {
-    auto total_ram_gigabytes = memtotal_ / std::pow(1024, 2);
-    int  used_ram_percentage = 100 * (memtotal_ - memfree_) / memtotal_;
-    auto used_ram_gigabytes = (memtotal_ - memfree_) / std::pow(1024, 2);
-    auto available_ram_gigabytes = memfree_ / std::pow(1024, 2);
+
+  unsigned long memtotal = meminfo_["MemTotal"];
+  unsigned long memfree;
+  if (meminfo_.count("MemAvailable")) {
+    // New kernels (3.4+) have an accurate available memory field.
+    memfree = meminfo_["MemAvailable"];
+  } else {
+    // Old kernel; give a best-effort approximation of available memory.
+    memfree = meminfo_["MemFree"] + meminfo_["Buffers"] + meminfo_["Cached"] +
+              meminfo_["SReclaimable"] - meminfo_["Shmem"];
+  }
+
+  if (memtotal > 0 && memfree >= 0) {
+    auto total_ram_gigabytes = memtotal / std::pow(1024, 2);
+    int  used_ram_percentage = 100 * (memtotal - memfree) / memtotal;
+    auto used_ram_gigabytes = (memtotal - memfree) / std::pow(1024, 2);
+    auto available_ram_gigabytes = memfree / std::pow(1024, 2);
 
     getState(used_ram_percentage);
     label_.set_markup(fmt::format(format_,
@@ -33,7 +45,6 @@ auto waybar::modules::Memory::update() -> void {
 }
 
 void waybar::modules::Memory::parseMeminfo() {
-  int64_t       memfree = -1, membuffer = -1, memcache = -1, memavail = -1;
   std::ifstream info(data_dir_);
   if (!info.is_open()) {
     throw std::runtime_error("Can't open " + data_dir_);
@@ -44,23 +55,9 @@ void waybar::modules::Memory::parseMeminfo() {
     if (posDelim == std::string::npos) {
       continue;
     }
+
     std::string name = line.substr(0, posDelim);
     int64_t     value = std::stol(line.substr(posDelim + 1));
-
-    if (name.compare("MemTotal") == 0) {
-      memtotal_ = value;
-    } else if (name.compare("MemAvailable") == 0) {
-      memavail = value;
-    } else if (name.compare("MemFree") == 0) {
-      memfree = value;
-    } else if (name.compare("Buffers") == 0) {
-      membuffer = value;
-    } else if (name.compare("Cached") == 0) {
-      memcache = value;
-    }
-    if (memtotal_ > 0 && (memavail >= 0 || (memfree > -1 && membuffer > -1 && memcache > -1))) {
-      break;
-    }
+    meminfo_[name] = value;
   }
-  memfree_ = memavail >= 0 ? memavail : memfree + membuffer + memcache;
 }