Bugzilla

Here's a profile of those STR, captured in current Nightly -- notice the 3-4second periods of jank in the parent process:
https://share.firefox.dev/47UKDz7

(Unfortunately I can' t capture a "good" profile from Nightly 2018-10-05 for comparison, because https://profiler.firefox.com/ doesn't load in that build. Maybe it's possible but needs special setup; not sure.)

evilpie: could you take a look here perhaps? I think your bug 1493150 seems like the only thing in that push range that might've influenced sessionstore JSON-serialization jank-time.  (It looks like bug 1493150 was meant to be an optimization, but I'm guessing that maybe there could be edge cases where it made things slower, and this was one of them.)

If that patch is indeed the regressor, I wonder if there are any obvious improvements to the approach in that patch that could make things better here; or, I wonder if there are changes we could make on the frontend to get a faster operation here (as good as or better as we had on 2018-10-05).

Here's a profile of those STR, captured in current Nightly -- notice the 3-4second periods of jank in the parent process:
https://share.firefox.dev/47UKDz7

(Unfortunately I can' t capture a "good" profile from Nightly 2018-10-05 for comparison, because https://profiler.firefox.com/ doesn't load in that build. Maybe it's possible but needs special setup; not sure.)

evilpie: could you take a look here perhaps? I think your bug 1493150 seems like the only thing in that push range that might've influenced sessionstore JSON-serialization jank-time.  (It looks like bug 1493150 was meant to be an optimization, but I'm guessing that maybe there could be edge cases where it made things slower, and this was one of them.)

If that patch is indeed the regressor, I wonder if there are any obvious improvements to the approach in that patch that could make things better here; or, I wonder if there are changes we could make on the frontend to get a faster operation here (as good as or better as we had on 2018-10-05).

([EDITING to add a note]: I'm bringing this up over here rather than on the dupe-target because I don't want to derail that bug any more than I already have. :)  We probably want to keep that bug focused on "how can we redesign sessionstore-serialization overall so that things are faster"; whereas this possible JS-engine-regression is also worth investigating but is kind of a separate discussion.)