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Re: Moving /tmp to tmpfs makes it useless

On Fri, 25 May 2012, Salvo Tomaselli wrote:
> > Because paging out a couple Gigabytes is veeeeeery different from
> > writing a couple Gigabytes to disk, of course.
> Yes because writing that on disk will only block the thread performing the 
> write, not every thread that tries to allocate memory.

What IO scheduler are you using?  It must not be CFQ.  CFQ will happly
screw it up and stall both readers and writers when the number of dirty
pages gets too large (which will happen if you write a gigabyte file to

Either that, or you're cheating and your backend devices are simply "fast
enough" that it doesn't matter (fast RAID or fast SSD).

The real question is: what does it better under CFQ+IO contention?
Several threads doing filesystem IO, or the swapper?  Hint: it is not an
easy question to answer because it depends on the load, type of load,
and backend device.

  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh

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