Wednesday, 20 January 2016

Re: RFC on Cloud Images: Make /tmp a tmpfs

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On 14/01/16 18:53, Steve Langasek wrote:
> On Thu, Jan 14, 2016 at 03:54:30PM +0200, Dustin Kirkland wrote:
>>> As a data point, I used to have my /tmp on tmpfs while I still had a
>>> spinning disk, in order to address the power usage issues of disk flushing.
>>> I found it to be a least-bad option which led to serious degradation of
>>> desktop interactivity in the face of even moderate memory usage (at the
>>> time, with 4GB RAM), and not because of excessive /tmp usage.
>
>>> And as others in this thread have noted, this same problem can occur in
>>> cloud instances.
>
>> Definitely. /tmp on tmpfs saves energy when you have a spinning HDD,
>> and extends the life of your SSD by reducing the number of NAND flash
>> writes!
>
> Sorry, I seem to have not made my point clear. I said this was a *least
> bad* option when running on an HDD. I ditched it soon after switching to an
> SSD, because it had a horrible impact on desktop interactivity. It might
> extend the life of the SSD, but it was certainly shortening mine.
>
> The correct fix for writing to /tmp causing excessive flushes to disk is to
> *fix the thing that's causing flushing to disk*. Trying to dodge by moving
> /tmp into tmpfs just shuffles the problem around.
>
+1 on that. We do have various tools for identifying badly behaving
applications that do excessive flushes, for example fnotifystat [1]
which I developed to track down bad apps on the phone.

[1] http://kernel.ubuntu.com/~cking/fnotifystat

Colin
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