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+#+TITLE: RAM failures: How to detect and fix
+#+DATE: <2022-10-26 Wed>
+#+LANGUAGE: en
+
+* RAM failures: How to detect and fix
+
+#+BEGIN_abstract
+If your system break in unexpected ways and you can't understand why it
+might be the RAM issue. In this article, I will try to explain why RAM
+is getting broken, how to detect it, and how to potentially fix it
+without going too deep into details.
+#+END_abstract
+
+#+ATTR_HTML: :loading lazy
+[[file:../../../public/images/thinkpad_ram_fail.jpg]]
+
+I've started struggling with segfaults and other problems more often
+after years of using my laptop. It was not critical, but annoying and it
+turned out that the problem was a broken ram module. I tested it and
+then after figuring out that it was broken I removed it completely. I
+had only 2GiB of RAM available after that, but I got to the conclusion
+that 2GiB is enough for me to do the work if to apply some optimizations
+to my GNU+Linux system.
+
+** What RAM is used for
+RAM is used to execute and store program memory. When you run the binary
+all CPU instructions are being placed into RAM and then all that
+instructions are being read sequentially one after another. While
+executing your program it will store intermediate results such as
+storing variables, data structures, and so on into RAM. After finishing
+your program RAM is cleared from program instructions and intermediate
+results of execution of these instructions.
+
+[[[https://en.wikipedia.org/wiki/Random-access_memory][Wikipedia: Random-access memory]]]
+
+** Why RAM can be damaged
+I can't say why exactly it can be damaged, overheating is probably one
+of the factors. There is a chance that RAM itself is not damaged at all.
+Actually it looks like that it breaks rarely. What can be "damaged" is
+RAM module contacts and it can be easily fixed. What you need to do is
+to take out ram modules and use an eraser to clean its contacts. But how
+to understand that you have a problem in the first place?
+
+** How to understand that RAM is broken
+The most expected way to see RAM fail is [[https://computerhope.com/beep.htm][BIOS signalling]] that it is
+broken. It should beep using PC Speaker a special signal. You can read
+your motherboard manual to understand what does it mean. Usually it
+means that computer won't start with "completely" broken RAM module.
+
+If system loads just fine, but you experience problems along the way
+such as random segfaults and programs crashes, kernel panics and so on,
+you might have broken segments of RAM. To detect such segments you can
+use several programs listed below. RAM checking is usually not a fast
+process, so you will probably need to left your device running for
+several hours.
+
+*** Memtest86+
+Memtest86+ runs from grub menu before your OS. It needs to run in such
+way because it needs whole range of RAM and your system can use a range
+of ram and would not allow to properly check it. It runs a lot of checks
+and checks every segment of your ram. While checking it logs the list of
+broken segments that you can write down.
+
+You can install it using your GNU+Linux package manager such as apt. The
+package is usually called ~memtest86+~. But there is a small caveat. If
+you use old version it wont work on UEFI systems.
+
+If it doesn't work you can download memtest86+ newer version
+distribution to your usb stick and load memtest from that. It should
+work on UEFI and BIOS systems. It can be downloaded from offical
+website.
+
+[[[https://memtest.org/][Official Website]]]
+
+*** Memtester
+It has the same purpose as memtest86+, but it runs while your system is
+running, so it doesn't check whole RAM range, but only specified free
+ram available at your system at the moment of running this program. It
+can be installed using your package manager of choice by typing
+~memtester~ as package name.
+
+[[[https://pyropus.ca./software/memtester/][Official Website]]]
+
+** How to fix broken RAM
+#+ATTR_HTML: :loading lazy
+[[file:../../../public/images/thinkpad_ram_repair.jpg]]
+
+First of all, if memtest86+ or(and) memtester doesn't show you any
+error, congratulations! You don't have any problems with your RAM.
+
+If it shows small amount of errors like one or two, you can let Linux
+Kernel ignore such segments of RAM, so programs doesn't use such broken
+segments and programs work stable all the time. You need to use for that
+~memmap~ kernel argument in your grub configuration. For example:
+~memmap=0x100000$762ce9c38420,0x100000$34e03060,0x100000$87fce060,0x100000$23c63060,0x100000$87b6c060~. There
+is also grub config unit called ~GRUB_BADRAM~, but it looks like it is
+deprecated and memmap is preffered.
+
+For more details about blacklisting bad segments of RAM read [[https://unix.stackexchange.com/questions/75059/how-to-blacklist-a-correct-bad-ram-sector-according-to-memtest86-error-indicati][this
+comprehensive Stack Overflow answer]].
+
+If it shows huge amount of errors, like many thousand, it means that
+probably one of your sticks of RAM are broken. To detect which one is
+broken exactly you can probably figure it out looking at addresses or
+running another test using specific stick(s) of RAM and seeing if errors
+are gone.
+
+Be aware, that if you left with one RAM stick there is a chance, that it
+will only boot in specific RAM slot. Read your motherboard manual if
+something doesn't work.
+
+If you have a RAM memory stick with tons of errors, you can try to
+repair it. I can't tell how exactly it is being done and why it is done
+in the way it should be done. You can find videos on fixing RAM sticks
+on YouTube and other resources. Here is [[https://youtu.be/KVR91p-Bd6M][the link to one of such videos]].
+
+** RAM Optimizations of GNU+Linux system
+If your RAM was broken and you left with much less memory that you
+expected, don't run and buy new RAM sticks. There is a chance that even
+with less RAM the system will work completely fine. Linux is pretty good
+at working on low end machines and it has different ways to handle lack
+of memory. It is often situation to have devices that outperform their
+tasks in modern world, like working on gaming laptop with very powerful
+CPU and GPU, that are used mostly to render text in a text editor.
+
+*** Swap
+Swap is a partiton on your hard drive that is being used in situation
+when there is no RAM left. It is used for other reasons too and such
+partition is recommended to have on most GNU+Linux systems.
+
+You can configure how often linux system will use swapp changing
+~swappiness~. You can read about changing that setting and to learn about
+swap in general in the link below.
+
+[[[https://wiki.archlinux.org/title/swap][Arch Linux Wiki: Swap]]]
+
+*** Zram
+Zram is something that stays in between RAM and Swap in terms of
+performance. It helps your system to stay performant if it uses swap a
+lot, but it increases the CPU usage because of that. I use Zram on a
+machine with 2GiB of RAM and 16GiB swap and it works great even with
+many programs opened at the same time (text editor, browser, docker
+container, messanger).
+
+[[[https://wiki.archlinux.org/title/Improving_performance#zram_or_zswap][Arch Linux Wiki: Zram]]]
+
+*** Less bloat software
+Also as alternative way you can simply use less bloat software, so you
+don't need so much RAM in the first place. In many cases good software
+doesn't require a lot of RAM, but bad software always leak memory, so
+you would need many GiBs of RAM to use it properly. The most bloated
+software is a web-browser such as chromium and firefox and browser-based
+apps done in electron such as Slack, VSCode and other proprietary
+products.
+
+** Conclusions
+Now you have directions about what to do when you suspect RAM
+failure. That knowledge can also be used for testing when you buy used
+memory sticks from someone else.
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