819489 - [Shutdown] Style sheet take ~50ms to release during shutdown

Status: NEW

(Core :: CSS Parsing and Computation, defect)

Description

[Benoit Girard (:BenWa)]

Profiles report:
http://people.mozilla.com/~bgirard/startup_report/report.html#nsCSSStyleSheet::~nsCSSStyleSheet

This currently list 10 shutdown profiles sorted from longest to shortest time spent in nsCSSStyleSheet::~nsCSSStyleSheet recorded on my system. Click on the profile will preview the profile + highlight the function.

Looks like a lot of the time is spent in free and related memory management function.

Comment 1

[Boris Zbarsky [:bzbarsky]]

This isn't object model stuff; this is basic style system data structures...

We've got free() calls for all the rules, their declarations, the selector linked lists (one free per node), the arrays stored in CSSDeclaration, and the various heap-allocated things hanging out in nsCSSValues. :(

Comment 2

[(no longer active)]

Can we allocate that stuff from arenas?

/me takes off the arenas-solve-everything hat

Comment 3

[Boris Zbarsky [:bzbarsky]]

We can try.  That does get into lifetime + CSSOM + DOM issues a bit.  :(

Comment 4

[David Baron :dbaron:]

bug 691216 would also help here.

Comment 5

[Benoit Girard (:BenWa)]

Attachment: Time spent

I have been receiving several profiles lately where there's over 1 second spent in this function. Here's the heavy leaf attach and a profile here:

http://people.mozilla.com/~bgirard/cleopatra/?report=e4bd2afaa201f68f1c5ebd934cf5b66e863c2e3b#report=e4bd2afaa201f68f1c5ebd934cf5b66e863c2e3b&search=Style
Note the resolution is 10ms

Comment 6

[Andrew McCreight [:mccr8]]

For what its worth, I've seen large CC pauses caused by the destructor for nsCSSStyleSheet (multiple ms for a single one) in bug 861449, and it was caused entirely by clearing arrays of Rules with thousands of elements.  For the CC pauses, this is easy enough to fix by switching over to a runnable that incrementally destroys the arrays, but of course that won't help with shutdown.