https://bugs.kde.org/show_bug.cgi?id=504287
Bug ID: 504287
Summary: KFileWidget is laggy on systems with many groups
Classification: Frameworks and Libraries
Product: frameworks-kio
Version: 6.14.0
Platform: Debian testing
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: Open/save dialogs
Assignee: kio-bugs-n...@kde.org
Reporter: bizy...@pm.me
CC: kdelibs-b...@kde.org
Target Milestone: ---
SUMMARY
When browsing directories with restricted (unreadable) subdirectories, such as
/tmp, the KDE file dialog has major UI lags if the system has many groups. This
affects file pickers in KDE and Qt apps, as well as the XDG portal.
This is caused by repeated calls to KUser::groups from the paint code, which
calls getgrouplist, which has to read and parse /etc/group and /etc/group.cache
over and over again. See the attached flame graph.
$ cat /etc/group.cache | wc -l
27634
$ du -h /etc/group.cache
752K /etc/group.cache
There should be no need for this: getgrouplist's result can be cached and
reused for the duration of the dialog's execution.
STEPS TO REPRODUCE
1. Build KIO with tests
2. Run
https://invent.kde.org/frameworks/kio/-/blob/master/tests/kfilewidgettest_gui.cpp
3. Navigate to /tmp or /
OBSERVED RESULT
Moving the mouse over restricted subdirectories (with the lock emblem) causes
UI freezes.
EXPECTED RESULT
No UI slowdowns.
SOFTWARE/OS VERSIONS
KDE Frameworks Version: 6.11, 6.14
ADDITIONAL INFORMATION
Relevant code:
* KFileItem::isReadable:
https://invent.kde.org/frameworks/kio/-/blob/85ac29eda6/src/core/kfileitem.cpp?page=2#L1292
* KUser::groups:
https://invent.kde.org/frameworks/kcoreaddons/-/blob/f67da202b88231/src/lib/util/kuser_unix.cpp#L328
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