[Bug 1533639] Re: [ubuntu-cpc] please make /tmp a tmpfs in RAM

[Robie Basak]

> * Performance - much faster read/write access to data in /tmp

Is this really true? Writes to /tmp will go to the page cache, which I
believe is an identical path whether /tmp is backed by disk or by tmpfs.
Similarly reads from /tmp will come from the page cache except where
pages have been evicted in the case of a disk-backed /tmp, which cannot
happen with tmpfs.

fsyncs on /tmp will be slower. Whether that's a problem depends on the
application. But do we need to use tmpfs to eliminate that? Is there a
better way of just swallowing syncs (eatmydata style), which would have
the same effect?

The big disadvantage of a tmpfs /tmp is that it cannot be paged out, and
thus puts pressure on available system RAM. One failure case is a
sysadmin expecting it to be backed to disk (and therefore be big), using
it for something temporary, and then killing the system due to memory
starvation.

> * Security - sensitive data would be cleared from memory on boot,
rather than written (leaked) to disk -- important for encryption
scenarios

If this is important then surely the user is encrypting the filesystem
on disk anyway?

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https://bugs.launchpad.net/bugs/1533639

Title:
  [ubuntu-cpc] please make /tmp a tmpfs in RAM

Status in livecd-rootfs package in Ubuntu:
  Triaged

Bug description:
  In Ubuntu, we clear /tmp on every boot.

  As such, on servers, by default /tmp should actually be a tmpfs
  entirely in RAM.

  This has several advantages, mainly:
   * Performance - much faster read/write access to data in /tmp
   * Security - sensitive data would be cleared from memory on boot, rather than written (leaked) to disk -- important for encryption scenarios

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