On 03/08/2016 09:58 AM, Derek Higgins wrote:
On 7 March 2016 at 18:22, Ben Nemec <openst...@nemebean.com> wrote:
On 03/07/2016 11:33 AM, Derek Higgins wrote:
On 7 March 2016 at 15:24, Derek Higgins <der...@redhat.com> wrote:
On 6 March 2016 at 16:58, James Slagle <james.sla...@gmail.com> wrote:
On Sat, Mar 5, 2016 at 11:15 AM, Emilien Macchi <emil...@redhat.com> wrote:
I'm kind of hijacking Dan's e-mail but I would like to propose some
technical improvements to stop having so much CI failures.
1/ Stop creating swap files. We don't have SSD, this is IMHO a terrible
mistake to swap on files because we don't have enough RAM. In my
experience, swaping on non-SSD disks is even worst that not having
enough RAM. We should stop doing that I think.
We have been relying on swap in tripleo-ci for a little while. While
not ideal, it has been an effective way to at least be able to test
what we've been testing given the amount of physical RAM that is
available.
Ok, so I have a few points here, in places where I'm making
assumptions I'll try to point it out
o Yes I agree using swap should be avoided if at all possible
o We are currently looking into adding more RAM to our testenv hosts,
it which point we can afford to be a little more liberal with Memory
and this problem should become less of an issue, having said that
o Even though using swap is bad, if we have some processes with a
large Mem footprint that don't require constant access to a portion of
the footprint swaping it out over the duration of the CI test isn't as
expensive as it would suggest (assuming it doesn't need to be swapped
back in and the kernel has selected good candidates to swap out)
o The test envs that host the undercloud and overcloud nodes have 64G
of RAM each, they each host 4 testenvs and each test env if running a
HA job can use up to 21G of RAM so we have over committed there, it
this is only a problem if a test env host gets 4 HA jobs that are
started around the same time (and as a result a each have 4 overcloud
nodes running at the same time), to allow this to happen without VM's
being killed by the OOM we've also enabled swap there. The majority of
the time this swap isn't in use, only if all 4 testenvs are being
simultaneously used and they are all running the second half of a CI
test at the same time.
o The overcloud nodes are VM's running with a "unsafe" disk caching
mechanism, this causes sync requests from guest to be ignored and as a
result if the instances being hosted on these nodes are going into
swap this swap will be cached on the host as long as RAM is available.
i.e. swap being used in the undercloud or overcloud isn't being synced
to the disk on the host unless it has to be.
o What I'd like us to avoid is simply bumping up the memory every time
we hit a OOM error without at least
1. Explaining why we need more memory all of a sudden
2. Looking into a way we may be able to avoid simply bumping the RAM
(at peak times we are memory constrained)
as an example, Lets take a look at the swap usage on the undercloud of
a recent ci nonha job[1][2], These insances have 5G of RAM with 2G or
swap enabled via a swapfile
the overcloud deploy started @22:07:46 and finished at @22:28:06
In the graph you'll see a spike in memory being swapped out around
22:09, this corresponds almost exactly to when the overcloud image is
being downloaded from swift[3], looking the top output at the end of
the test you'll see that swift-proxy is using over 500M of Mem[4].
I'd much prefer we spend time looking into why the swift proxy is
using this much memory rather then blindly bump the memory allocated
to the VM, perhaps we have something configured incorrectly or we've
hit a bug in swift.
Having said all that we can bump the memory allocated to each node but
we have to accept 1 of 2 possible consequences
1. We'll env up using the swap on the testenv hosts more then we
currently are or
2. We'll have to reduce the number of test envs per host from 4 down
to 3, wiping 25% of our capacity
Thinking about this a little more, we could do a radical experiment
for a week and just do this, i.e. bump up the RAM on each env and
accept we loose 25 of our capacity, maybe it doesn't matter, if our
success rate goes up then we'd be running less rechecks anyways.
The downside is that we'd probably hit less timing errors (assuming
the tight resources is whats showing them up), I say downside because
this just means downstream users might hit them more often if CI
isn't. Anyways maybe worth discussing at tomorrows meeting.
+1 to reducing the number of testenvs and allocating more memory to
each. The huge number of rechecks we're having to do is definitely
contributing to our CI load in a big way, so if we could cut those down
by 50% I bet it would offset the lost testenvs. And it would reduce
developer aggravation by about a million percent. :-)
Also, on some level I'm not too concerned about the absolute minimum
memory use case. Nobody deploying OpenStack in the real world is doing
so on 4 GB nodes. I doubt 99% of them are doing so on less than 32 GB
nodes. Until we have composable services, I don't know that we can
support the 4 GB use case anymore. We've just added too many services
to the overcloud.
We discussed this at today's meeting but never really came to a
conclusion except to say most people wanted to try it. The main
objection brought up was that we shouldn't go dropping the nonha job,
that isn't what I was proposing so let me rephrase here and see if we
can gather +/-1's
I'm proposing we redeploy our testenvs with more RAM allocated per
env, specifically we would go from
5G undercloud and 4G overcloud nodes to
6G undercloud and 5G overcloud nodes to
In addition to accommodate this we would reduce the number of env's
available from 48 (the actually number varies from time to time) to 36
(3 envs per host)
No changes would be happening on the jobs we actually run
The assumption is that with the increased resources we would hit less
false negative test results and as a result recheck jobs less (so the
25% reduction in capacity wouldn't hit us as hard as it might seem),
we also may not be able to easily undo this if it doesn't work out as
once we start merging things that use the extra RAM it will be hard to
go back.
+1, so many false negatives today. I think it would also be useful to
add a memory usage/free report at the end of the CI run. This can be
used to gauge how new changes are affecting consumption.
That said though, keeping service memory usage under control is still
valuable and we should figure out why Swift is using so much memory when
it's not under much load at all. That's actually the undercloud, so
it's sort of tangential to this discussion.
<snip/>
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