RAM usage calculation.

[jokerekv2]

Can someone explain to me how ram usage is calculated?
I noticed a difference between htop and btop scores and hence this question.

[aristocratos]

@jokerekv2

Hi, I'm assuming you mean for linux?

Memory stats are read from /proc/meminfo.
But since /proc/meminfo doesn't provide a "used" metric, it's calculated from total memory - available memory.
So "used memory" = "non available memory".
Haven't look at how htop calculates this but the current calculation is what made most sense to me.

The code in question:

btop/src/linux/btop_collect.cpp

Lines 729 to 766 in e2668c6

	//? Read memory info from /proc/meminfo
	ifstream meminfo(Shared::procPath / "meminfo");
	if (meminfo.good()) {
	bool got_avail = false;
	for (string label; meminfo >> label;) {
	if (label == "MemFree:") {
	meminfo >> mem.stats.at("free");
	mem.stats.at("free") <<= 10;
	}
	else if (label == "MemAvailable:") {
	meminfo >> mem.stats.at("available");
	mem.stats.at("available") <<= 10;
	got_avail = true;
	}
	else if (label == "Cached:") {
	meminfo >> mem.stats.at("cached");
	mem.stats.at("cached") <<= 10;
	if (not show_swap and not swap_disk) break;
	}
	else if (label == "SwapTotal:") {
	meminfo >> mem.stats.at("swap_total");
	mem.stats.at("swap_total") <<= 10;
	}
	else if (label == "SwapFree:") {
	meminfo >> mem.stats.at("swap_free");
	mem.stats.at("swap_free") <<= 10;
	break;
	}
	meminfo.ignore(SSmax, '\n');
	}
	if (not got_avail) mem.stats.at("available") = mem.stats.at("free") + mem.stats.at("cached");
	mem.stats.at("used") = totalMem - mem.stats.at("available");
	if (mem.stats.at("swap_total") > 0) mem.stats.at("swap_used") = mem.stats.at("swap_total") - mem.stats.at("swap_free");
	}
	else
	throw std::runtime_error("Failed to read /proc/meminfo");
	meminfo.close();