[Bug 858714] [NEW] default swap allocation makes system unresponsive

[Andreas Kostyrka]

Public bug reported:

On my system with 8GB RAM, the automatic created swap size if 4GB. On a
typical hdd setup, filling this 4GB swap can take over an hour. During
this time, the system is very unresponsive, till the out-of-memory
killer can clean up the issue.

Please consider that swap has a tendency to be accessed via random
patterns, and not sequentially, hence no matter how fast the hdd, there
is basically a limited number of "transactions" available, hence an
acceptable duration of trashing is not linear to the RAM size in any
way.

All of this applies only to hdd based swap, any random-access storage
(SSD, flash) has this problem not (mostly, if the IO bandwidth is to
slow, an overly huge swap can again become problematic)

So to give the user a much improved  experience, Ubuntu needs to limit
hdd swap size, and consider using compcache sized relatively to the RAM
size. I personally cannot recommend the right size (it certainly depends
a little bit on the hdd, and the overall system, as I've been using
compcache and SSD-based swap exclusively the last years. On LVM one can
get rid of the swap partition easily enough, but without LVM it would
leave me with an useless 4GB partition lying around).

Thanks

** Affects: base-installer (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/858714

Title:
  default swap allocation makes system unresponsive

Status in “base-installer” package in Ubuntu:
  New

Bug description:
  On my system with 8GB RAM, the automatic created swap size if 4GB. On
  a typical hdd setup, filling this 4GB swap can take over an hour.
  During this time, the system is very unresponsive, till the out-of-
  memory killer can clean up the issue.

  Please consider that swap has a tendency to be accessed via random
  patterns, and not sequentially, hence no matter how fast the hdd,
  there is basically a limited number of "transactions" available, hence
  an acceptable duration of trashing is not linear to the RAM size in
  any way.

  All of this applies only to hdd based swap, any random-access storage
  (SSD, flash) has this problem not (mostly, if the IO bandwidth is to
  slow, an overly huge swap can again become problematic)

  So to give the user a much improved  experience, Ubuntu needs to limit
  hdd swap size, and consider using compcache sized relatively to the
  RAM size. I personally cannot recommend the right size (it certainly
  depends a little bit on the hdd, and the overall system, as I've been
  using compcache and SSD-based swap exclusively the last years. On LVM
  one can get rid of the swap partition easily enough, but without LVM
  it would leave me with an useless 4GB partition lying around).

  Thanks

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