Since 7/12, ghost windows have been reported as 0, which is bad.
This is bad because we're trying to track no regressions in this metric for 57.
(Temporarily giving to mccr8 as he's the most connected to this issue right now)
Eric said he'd look at it.
We know that ghost window reporting still works when generating memory reports so at least that part isn't broken. That implies that the logic to periodically calculate ghost windows triggered by windows closing  or cycle collection finishing  is somehow broken. Before we just always calculated the value when telemetry asked for it, but now we depend on a cached value from the periodic calcuation. Andrew pointed out a few spikes on telemetry  where we see a drop on 7/1 (corresponding with bug 1375281 which switched to request idle callback) and rise on 7/6 (corresponding with bug 1377767 which fixed us using an old api for idle callback), so those are probably red herrings. It's pretty clear that bug 1376038 is the regression.  http://searchfox.org/mozilla-central/rev/8a61c71153a79cda2e1ae7d477564347c607cc5f/dom/base/nsWindowMemoryReporter.cpp#611-634  http://searchfox.org/mozilla-central/rev/8a61c71153a79cda2e1ae7d477564347c607cc5f/dom/base/nsWindowMemoryReporter.cpp#636-648  https://mzl.la/2w1fU1E
Created attachment 8891105 [details] [diff] [review] Always update cached ghost window count Currently the cached count is only updated if a table was passed in to keep track of the window IDs. This changes the behavior to always update the count regardless of whether a table is passed in. MozReview-Commit-ID: EkfzLemVJyV
https://hg.mozilla.org/integration/mozilla-inbound/rev/c8f400fc23a72fab985d3baa08b5cc22d2190326 Bug 1384337 - Always update cached ghost window count. r=mccr8
I'm seeing ghost windows in telemetry again. Thanks, Eric.
Backed out from mozilla-central along with bug 1376038 to help with the investigation of bug 1388111. https://hg.mozilla.org/integration/mozilla-inbound/rev/69b75c23e0301ffda2e2bb5bb40d4e803ac6e242 Note that the status is a little screwy here because Beta56 still has the patches in question.
also backedout from m-c https://hg.mozilla.org/mozilla-central/rev/69b75c23e030
Hey Eric, what's the plan here, reland?
This bug is "fixed" in the sense that ghost window telemetry is working. If erahm relands, I assume he'll just roll that into his patch for the other bug.
Yeah I can look into relanding tomorrow. Keeping ni for now.
Okay as :mccr8 noted I'll just roll this up into bug 1376038.