1866161 - Navigating to specific markdown files on github is extremely slow

Status: RESOLVED FIXED

(Core :: DOM: Core & HTML, defect)

Description

[Markus Stange [:mstange]]

Steps to reproduce:

1. Go to https://github.com/jrmuizel/github-slow-md
2. Click on go-slow.md

Expected results:
The contents of the markdown file should appear quickly. (They do in Chrome.)

Actual results:
It takes thirty seconds or more.

Profile: https://share.firefox.dev/3SPoNsN

Comment 1

[Jan Jaeschke [:jjaschke]]

To add to that: It gets massively worse if you select one of the JS code boxes and try to view the source for the selection. That took several minutes on my machine (on a M1 Mac; loading the md file itself only took ~5s instead of the reported 30s).

I have created a few-second-snapshot profile. That profile shows significant time is spent in this comparator, which calls nsINode::ComparePoints_deprecated(), all triggered from nsIFrame::IsFrameSelected() while reflowing.

It looks from the profile as if nsIFrame::IsFrameSelected() is called twice during reflow. Maybe it's possible to add some caching there (that feels like fighting the symptoms though, and also won't fix the original issue)?

:smaug, wdyt?

Comment 2

[Emilio Cobos Álvarez [:emilio]]

Attachment: Bug 1866161 - Stop propagating directionality earlier. r=smaug,peterv

If the element already has the right directionality we don't need to
traverse the whole subtree.

Clean-up surrounding code a little bit while at it.

Comment 3

[Emilio Cobos Álvarez [:emilio]]

https://treeherder.mozilla.org/jobs?repo=try&revision=1d8941ac82f8d8483bb9f0f7a78484e20df3c05e

Comment 4

[Olli Pettay [:smaug][[e-mail]]]

oh, the needinfo was for another issue. Jan, please file another bug for that.

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/9951dfb718b3
Stop propagating directionality earlier. r=smaug

Comment 6

[Norisz Fay [:noriszfay]]

https://hg.mozilla.org/mozilla-central/rev/9951dfb718b3