Seeing another of your post I guess you are using zram. So that will be my assumption here.
I did the experience to install zram and consume lot of memory, and I got the same output of smem than you. smem does not take into account zram into its counting, it only uses /proc/meminfo to compute its value, and if you look and try to understand the code you will see that the zram RAM occupation is gets in the end counted under the noncache column of the kernel dynamic memory line.
Further investigations
Following my gut feeling that zram was behind this behavious, I setted up a VM with similar spec as your machine: 4 GB RAM and 2 GB zram swap, no swap file.
I have loaded the VM with heavy weight applications and got the following state:
huygens@ubuntu:~$ smem -wt -K ~/vmlinuz-3.2.0-38-generic.unpacked -R 4096M
Area Used Cache Noncache
firmware/hardware 130717 0 130717
kernel image 13951 0 13951
kernel dynamic memory 1063520 922172 141348
userspace memory 2534684 257136 2277548
free memory 451432 451432 0
----------------------------------------------------------
4194304 1630740 2563564
huygens@ubuntu:~$ free -m
total used free shared buffers cached
Mem: 3954 3528 426 0 79 858
-/+ buffers/cache: 2589 1365
Swap: 1977 0 1977
As you can see free reports 858 MB cache memory and that is also what smem seems to report within the cached kernel dynamic memory.
Then I further stressed the system using Chromium Browser. At the beginning, it was only have 83 MB of swap used. But then after a few more tabs opened, the swap switch quickly to almost it's maximum and I experienced OOM! zram has really a dangerous side where wrongly configured (too big sizes) it can quickly hit you back like a trebuchet-like mechanism.
At that time I had the following outputs:
huygens@ubuntu:~$ smem -wt -K ~/vmlinuz-3.2.0-38-generic.unpacked -R 4096M
Area Used Cache Noncache
firmware/hardware 130717 0 130717
kernel image 13951 0 13951
kernel dynamic memory 1355344 124072 1231272
userspace memory 961004 36456 924548
free memory 1733288 1733288 0
----------------------------------------------------------
4194304 1893816 2300488
huygens@ubuntu:~$ free -m
total used free shared buffers cached
Mem: 3954 2256 1698 0 4 132
-/+ buffers/cache: 2118 1835
Swap: 1977 1750 227
See how the kernel dynamic memory (columns cache and non-cache) look like inverted? It is because in the first case, the kernel had "cached" memory such as reported by free but then it had swap memory held by zram which smem does not know how to compute (check smem source code, zram occupation is not reported in /proc/meminfo, this it is not computed by smem which does simple "total kernel mem" - "type of memory reported by meminfo that I know are cache", what it does not know is that in the computed total kernel mem it has added the size of the swap which is in RAM!)
When I was in this state, I activated a hard disk swap and turned off the zram swap and I reset the zram devices: echo 1 > /sys/block/zram0/reset.
After that the noncache kernel memory melted like snow in summer and returned to "normal" value.
Conclusion
smem does not know about zram (yet) maybe because it is still staging and thus not part of /proc/meminfo which reports global parameters (like (in)active pages size, total memory) and then only report on a few specific parameters. smem identified a few of this specific parameters as "cache", sum them up and compare that to total memory. Because of that zram used memory gets counted in the noncache column.
Note: by the way, in modern kernel, meminfo reports also the shared memory consumed. smem does not take that yet into account, so even without zram the output of smem is to consider carefully esp. if you use application that make big use of shared memory.
References used:
I'm not sure everything you need is exposed in /proc/meminfo's output so that you can calculate MemTotal yourself. From the Linux Kernel's documentation proc.txt file:
excerpt
MemTotal: Total usable ram (i.e. physical ram minus a few reserved
bits and the kernel binary code)
dmesg
If you look through either the output of dmesg or the log file /var/log/dmesg you can find the following information:
$ grep -E "total|Memory:.*available" /var/log/dmesg
[ 0.000000] total RAM covered: 8064M
[ 0.000000] On node 0 totalpages: 2044843
[ 0.000000] Memory: 7970012k/9371648k available (4557k kernel code, 1192276k absent, 209360k reserved, 7251k data, 948k init)
I believe this information can be used to determine MemTotal. This blog post covers it in more details, it's titled: Understanding “vmalloc region overlap”. Also this post, which provides some additional info, titled: Anatomy of a Program in Memory.
References
Best Answer
Memory capacity in DIMMs is measured in powers of two, so a claimed RAM capacity of “128 giga-something” is 128 GiB which is 134,217,728 kiB.
/proc/meminfoalso measures memory in powers of two, so theMemTotalvalue of 131,927,808 can be compared with 134,217,728 and is safely less.MemTotalis the total installed physical memory minus whatever is reserved by the system firmware and the kernel binary. Your boot log should contain a line of the formwhich will indicate exactly how much is reserved by the system (the “reserved” figure) and the kernel binary (the “kernel code” figure).