Follows-up from T167885: Regression: Backend Save Timing raised by about 50%
Restarting a server causes APC to get cleared since it is part of the same process. While it might be nice to preserve it somehow, I think we've gotten used to this being the case and accepted this. It has also become an unfortunate, but regular habit, to restart HHVM when APC usage grows out of hand (given HHVM doesn't do LRU garbage collection and just lets itself OOM if not enough keys expire in time).
Regardless, the recent HHVM upgrade did *not* cause a memory drop like usual, but rather an increase.
- Verify that these events are correlated (e.g. not a coincidence). - Reproduce by restarting e.g. mwdebug servers.
- If true, verify what happens to APC values. Are they preserved? Assuming not, where is the memory going? Why is it not being released?
