2

Explanation

While working with older machine with swap on and 2 GB ram, I frequently encounter behaviour well described as freeze:

While all Q&A here focus mostly on

  • tweaking with sysctl vm.min_free_kbytes and vm.swappiness
  • other proposed solution tweaking oom_score and praying OOM works
  • setting up zram(swap compress)
  • shell scripts of various [1] sorts [2]
  • or even "advices" to buy more ram etc.

I find those solutions palliatives. I understand from reading kernel documentation, that even if OOM is made to behave, it can work in two "modes" for now:

  • either kills most memory hungry process (usually)
  • or kills memory 'offender' which is last process that actually tried to allocate memory.

Neither of this solution actually satisfies me. I came to conclusion that I DON'T want OOM to run killing either random or last process, yet I want to maintain system operational. I want to decide what to kill on my own, yet without tweaking oom_score for processes.

Questions

What I want to know/do, is:

  1. Have the situation changed/improved in never kernels (say 4.0 +)
  2. Have the situation changed in never Ubuntu (custom patches? 12.04 +)
  3. Regardless of those two questions, I'm open to suggestions, that were not yet mentioned in Q&A above.

  4. Regardless of those three questions above. I'm thinking about compiling own /bin/login binary, modified that:

    • it would allocate configurable amount of memory (ex. 8MB)
    • it would copy/fork configurable userspace TUI (ex. htop) (see this)
    • parent would put child process into suspend by sending it SIGTSTP (in order for it not to consume cpu), perhaps close child fd's.
    • parent would then send SIGTCONT to child only when user properly authenticated. Perhaps also restore child fd's if closed for security reasons,
    • this login-emergency binary would be executed by upstart/systemd or whatever init binary, running probably also with elevated permissions, to allow killing any desired process.

5. Does this approach seem sane or is this overkill? Any security flaws visible at glance?

Community
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JustMe
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  • If you're frequently having OOM issues, then you either need more RAM or you need to limit the number or size of programs you're running. Tweaking the OOM killer not to kill certain apps will just mean it has to find another app to kill to reclaim memory . Sending a SIGTSTP to a process will not help; it may stop using CPU time, but it's still sitting in virtual memory. – Karen B Jun 17 '16 at 17:54
  • That is almost like spending a month replacing a flat tire with a shopping cart wheel. My suggestion for systems with swap and little RAM is zram! It is very efficient in balancing swap efficiency. – Julie Pelletier Jun 17 '16 at 17:54
  • @KarenB this machine is at its limit, cannot support more RAM. JuliePelletier I find swap compression not a solution, with reasons too long for this comment and not relevant enough to add explanation for question, but thanks for suggestion anyways. – JustMe Jun 17 '16 at 17:55
  • What is more, I'm aware that in my case turning off OOM is rather needed (since I can't control what is going to be killed other that tweaking oom_scores, which is rather nonsense - if I expected to run out of memory I would free/run less programs before it happened, and wouldn't need to rely on OOM). – JustMe Jun 17 '16 at 18:02
  • You're still overlooking the obvious solutions: either get a bigger box or limit what is run on this box in the first place to decrease frequency of overallocation of memory. If you can't do either, you could improve swap perf by putting that on a faster/different disk than your root disk. – Karen B Jun 17 '16 at 18:07
  • No, I'm aware of this solution, and I do consider it. Yet let's assume for now it is a netbook, which is not my property - cannot insert drive, increase ram, and not eligible for upgrade by replacing with newer computer (which would be also time and money consuming process of selecting and buying one). – JustMe Jun 17 '16 at 18:10
  • If you can't do what's required (upgrade or replace the hardware) then don't run so much on it. You're pushing that little netbook way beyond what it's capable of. Linux isn't magic - it can't make, e.g., 16GB worth of apps fit into 2GB of RAM and a few more GB of swap. Start by using text-based clients (e.g. lynx/links for web, mutt for mail, vi or nano for text editing) rather than GUI memory-hogs (like firefox, thunderbird or evolution, or gedit etc)....in fact, kill X and use virtual consoles. – cas Jun 18 '16 at 07:41
  • Also, if money is the reason you can't replace the netbook, try scrounging / begging. There are lots of essentially worthless (in terms of price) 5+ year-old laptops gathering dust that would have much better specs (and upgradable RAM) than your netbook (an eeepc or similar, i presume)....and even geeks run out of things to repurpose old machines for (and often would rather give a laptop away than junk it) – cas Jun 18 '16 at 07:45
  • @cas haha I've never heard anyone so publicly encouraging begging as a method of upgrading gear or whatsoever :) I presume, if that was the case this might work for some people in some countries where people actually do give away stuff.This netbook(hp4160) has a little different history (clue:10h battery), but describing it here is little against site policy i'm afraid, and would be considered a spam, as it adds no value to the question. To make this comment a little useful - I wish big companies that sometimes destroy "computer scrap" offer sales, but due to legal and tax issues they dont :( – JustMe Jun 23 '16 at 16:39
  • There's nothing at all unusual about it - scrounging (and even begging for hardware) has a long tradition. Recycling is good, as is not allowing perfectly good but old machines to go to waste. even corps give away old equipment or sell for a nominal price (but usually with hard drives secure-erased or, more often, just removed and destroyed). BTW, my local linux user group maintains a hardware library of everything from parts like RAM, CPUs, GPUs, and disks to complete old name-brand servers for members to re-use/recycle for free. – cas Jun 24 '16 at 02:43

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