JS heap usage is leaking alarmingly and causing long-lived tabs to crawl

[ara4n]

I think this may be an artefact of the increasing number of E2E rooms, but on Chrome I got 6 minute's worth of "application unresponsive" warnings on unsleeping this morning interspersed with snatches of responsivity. It finally recovered; here's the JS console:

wedged-during-catchup.txt

It's possible that the JS heap had grown so huge that Chrome was swapping, given that it's been trying to generate a JS heap snapshot for the last 4 minutes now and has only got 32% of the way there.....

[ara4n]

(except the chrome process in question is 'only' 2.4GB RSZ, and the box isn't swapping :/)

[ara4n]

rather splendidly, the Inspector crashes about 5 minutes into trying to generate a heapdump, so i have no clue what state Chrome's in here :( Restarting...

[ara4n]

i think this is basically a memory leak - tabs which are older than a few days seem to be using loads of heap.

[ara4n]

i imagine this will be very problematic for electron too. may be related to #2109.

[richvdh]

let's not assume this is e2e until proven otherwise

[ara4n]

this is indeed just running out of heap, which is capped at 1.5GB on Chrome. It's been improved by various bugfixes by kegan but it's still a problem because we simply never reap old events from memory.

[ara4n]

closing as a dup of #2951