Slow shutdown with big file in /dev/shm

[Adam Jackson]

On 3/19/12 11:42 PM, Bojan Smojver wrote:
> Before I file a bug for this, I need to figure out which component may
> be doing this. If one creates a large file (several GB) in /dev/shm and
> shuts down, the system will take many minutes to shut down. Last message
> before hang is "Disabling swap".
>
> Not sure which component is doing that and why. The file will be gone on
> reboot anyway, so why not just nuke it...

Presumably because that file got paged out.

Think about it.  Disabling swap doesn't know that the file exists only 
on a RAM-based file system, and even if it did, doesn't know that we're 
about to shut down.  So swapoff has to assume that any pages currently 
in the swap area being disabled might be valuable, and has to read them 
back into memory.

Now as to why we disable swap on shutdown, I'm not really sure.  It 
certainly seems like useless work to me.

- ajax