totalSystemMemory

pub fn totalSystemMemory() TotalSystemMemoryError!u64 {
    switch (native_os) {
        .linux => {
            var info: std.os.linux.Sysinfo = undefined;
            const result: usize = std.os.linux.sysinfo(&info);
            if (std.os.linux.errno(result) != .SUCCESS) {
                return error.UnknownTotalSystemMemory;
            }
            // Promote to u64 to avoid overflow on systems where info.totalram is a 32-bit usize
            return @as(u64, info.totalram) * info.mem_unit;
        },
        .dragonfly, .freebsd, .netbsd => {
            const name = if (native_os == .netbsd) "hw.physmem64" else "hw.physmem";
            var physmem: c_ulong = undefined;
            var len: usize = @sizeOf(c_ulong);
            switch (posix.errno(posix.system.sysctlbyname(name, &physmem, &len, null, 0))) {
                .SUCCESS => return @intCast(physmem),
                .FAULT => unreachable,
                .PERM => unreachable, // only when setting values
                .NOMEM => unreachable, // memory already on the stack
                .NOENT => unreachable,
                else => return error.UnknownTotalSystemMemory,
            }
        },
        // whole Darwin family
        .driverkit, .ios, .maccatalyst, .macos, .tvos, .visionos, .watchos => {
            // "hw.memsize" returns uint64_t
            var physmem: u64 = undefined;
            var len: usize = @sizeOf(u64);
            switch (posix.errno(posix.system.sysctlbyname("hw.memsize", &physmem, &len, null, 0))) {
                .SUCCESS => return physmem,
                .FAULT => unreachable,
                .PERM => unreachable, // only when setting values
                .NOMEM => unreachable, // memory already on the stack
                .NOENT => unreachable, // constant, known good value
                else => return error.UnknownTotalSystemMemory,
            }
        },
        .openbsd => {
            const mib: [2]c_int = [_]c_int{
                posix.CTL.HW,
                posix.HW.PHYSMEM64,
            };
            var physmem: i64 = undefined;
            var len: usize = @sizeOf(@TypeOf(physmem));
            posix.sysctl(&mib, &physmem, &len, null, 0) catch |err| switch (err) {
                error.NameTooLong => unreachable, // constant, known good value
                error.PermissionDenied => unreachable, // only when setting values,
                error.SystemResources => unreachable, // memory already on the stack
                error.UnknownName => unreachable, // constant, known good value
                else => return error.UnknownTotalSystemMemory,
            };
            assert(physmem >= 0);
            return @as(u64, @bitCast(physmem));
        },
        .windows => {
            var sbi: windows.SYSTEM.BASIC_INFORMATION = undefined;
            const rc = windows.ntdll.NtQuerySystemInformation(
                .Basic,
                &sbi,
                @sizeOf(windows.SYSTEM.BASIC_INFORMATION),
                null,
            );
            if (rc != .SUCCESS) {
                return error.UnknownTotalSystemMemory;
            }
            return @as(u64, sbi.NumberOfPhysicalPages) * sbi.PageSize;
        },
        else => return error.UnknownTotalSystemMemory,
    }
}