Bug 118547 – Leaking most Documents when tab closing

• Component: WebCore Misc.
• Status: UNCONFIRMED

[Sangho Kim]

When a page is changed or closed, webkit doesn't release resources of current page.
It's very important thing on the device which has low memory.
I investigated of that. I found something.
Before merging http://trac.webkit.org/changeset/130817, The life cycle of CachedResourceLoader was with Document.
At this time, CachedResourceLoader was deleted when a page is changed or close.
After that, life cyccle was changed DocumentLoader for mainResources.
And CachedResourceLoader changed from OwnPtr to RefPtr on Document.
I think there are some memory leaks.
Please confirm.

[Alexey Proskuryakov]

Please post detailed steps to reproduce. What should I do to see the issue in Safari (debugging or additional logging is OK)?

[Brady Eidson]

Right - Your description sounds like you think there is a theoretical problem based on code inspection.

But have you actually observed misbehavior and - if so - how?

[Sangho Kim]

I didn't test by using Safari. I just tested on Qt. But I thought it might not be related with platform. It can't be wrong...
Reproduce step is simple. Put your log in constructor and destructor on Document, DocumentLoader, FrameLoader and CachedResourceLoader and do to change page. After page chaing, you can see only DocumentLoader was destroyed. The best way is CachedResourceLoader must be deleted for releasing memory.

[Brady Eidson]

I instrumented the c'tors and d'tors and ran some tests.

The problem isn't CachedResourceLoader - The problem is we're actually leaking most Documents.

Steps to reproduce:
1 - Print in Document c'tor and d'tor
2 - Open a window to a blank page.
3 - Navigate to http://example.iana.org
4 - Navigate to http://mysneakywebsite.com

The Document created when you navigate to http://example.iana.org is not destroyed.
Additionally - if you keep navigating around in this window, visiting dozens and dozens of sites - that Document is never destroyed.

In fact, only initial empty documents and "about:blank" documents seem to be getting destroyed.

[Brady Eidson]

I'll attach the patch I'm using and sample output.

[Brady Eidson]

Created attachment 206564 [details]
Patch for my debugging output

[Brady Eidson]

Created attachment 206565 [details]
Sample output with that patch

[Brady Eidson]

<rdar://problem/14430167>

[Brady Eidson]

I ran my original test in multiple web process mode.
Actually in single web process mode, it appears the Document does not leak indefinitely.  But there's still a bug:

Using some sequential test pages I put up on a server:
0x7fa32b548b40 - 1373673096.919025 - Constructing CachedResourceLoader
0x7fa32c005a00 - 1373673096.919108 - Constructing DocumentLoader ()
0x7fa32c034e00 - 1373673096.919625 - Constructing Document ()
0x7fa32e114170 - 1373673097.106312 - Constructing CachedResourceLoader
0x7fa32d00e200 - 1373673097.106356 - Constructing DocumentLoader (http://bradeeoh.com/test0.html)
0x7fa32c005a00 - 1373673097.454581 - Destroying DocumentLoader ()
0x7fa32d002000 - 1373673097.455927 - Constructing Document (http://bradeeoh.com/test0.html)
0x7fa32c034e00 - 1373673097.456086 - Destroying Document ()
0x7fa32b548b40 - 1373673097.456153 - Destroying CachedResourceLoader

---navigate---

0x7fa32e122360 - 1373673101.222555 - Constructing CachedResourceLoader
0x7fa32d00c400 - 1373673101.222602 - Constructing DocumentLoader (http://bradeeoh.com/test1.html)
0x7fa32d00e200 - 1373673101.387006 - Destroying DocumentLoader (http://bradeeoh.com/test0.html)
0x7fa32d027c00 - 1373673101.388695 - Constructing Document (http://bradeeoh.com/test1.html)

---navigate---

0x7fa32e633b50 - 1373673104.853812 - Constructing CachedResourceLoader
0x7fa32b84a000 - 1373673104.853854 - Constructing DocumentLoader (http://bradeeoh.com/test2.html)
0x7fa32d00c400 - 1373673105.019031 - Destroying DocumentLoader (http://bradeeoh.com/test1.html)
0x7fa32b850400 - 1373673105.019829 - Constructing Document (http://bradeeoh.com/test2.html)
0x7fa32d002000 - 1373673105.052540 - Destroying Document (http://bradeeoh.com/test0.html)
0x7fa32e114170 - 1373673105.052630 - Destroying CachedResourceLoader
0x7fa32d027c00 - 1373673105.052846 - Destroying Document (http://bradeeoh.com/test1.html)
0x7fa32e122360 - 1373673105.052896 - Destroying CachedResourceLoader

So while the Document for test0 isn't cleaned up after navigating to test1, it *is* cleaned up after navigating to test2.

This cycle repeats over and over.  Nav A -> Nav B -> Nav C (clean up Nav A and B).   Nav D (clean up Nav C).  Nav E -> Nav F (clean up Nav D and Nav E)
etc etc etc.

So yes, this seems like a bug for single web processes, but not a terribly tragic one.

[Sangho Kim]

Thanks for your test.
I have same results. I have one question.
Do you know why Document is not deleted as soon as page change
And How I fix the code if I want delete Document as soon as page close?

[Brady Eidson]

No I don't know yet.

Since there's no infinite leak here as originally reported, this isn't high enough priority for me to continue looking at right now.

You're free to continue looking into it!

[[e-mail]]

Doesn't the default history hold on to the last page in memory?  This could explain the behavior in comment #9

[Sangho Kim]

When tab closing, Documents wasn't deleted. Because of that, All resources was not deleted.