[dolphin] [Bug 476627] New: Loading of large directories abnormally slow after update

[Mircea Kitsune]

https://bugs.kde.org/show_bug.cgi?id=476627

            Bug ID: 476627
           Summary: Loading of large directories abnormally slow after
                    update
    Classification: Applications
           Product: dolphin
           Version: 23.08.2
          Platform: Other
                OS: Linux
            Status: REPORTED
          Severity: normal
          Priority: NOR
         Component: general
          Assignee: dolphin-bugs-null at kde.org
          Reporter: sonichedgehog_hyperblast00 at yahoo.com
                CC: kfm-devel at kde.org
  Target Milestone: ---

Created attachment 162900
  --> https://bugs.kde.org/attachment.cgi?id=162900&action=edit
fstab

SUMMARY
Large directories are now taking a ridiculous amount of time to load in
Dolphin. A folder with over 65.000 images would previously take roughly 15
seconds to finish loading, now it’s over 5 minutes. During this time I see 100%
of one CPU core being used, however I can’t find a root or user process doing
it and it’s not the Dolphin application itself… my hard drive keeps being read
at a rate of roughly 3 MB/s.

This only happens once per directory after boot, after a directory finishes
showing up it will load at normal speed until you reboot... this indicates the
problem may be related to caching. It’s definitely not a problem with my drive
and was introduced by a recent update, other operations such as using the 'ls'
command are just as fast only Dolphin appears to be affected.

STEPS TO REPRODUCE
You need a directory with a lot of files to see it clearly, at least 50.000 if
possible: Open it and the issue should be quickly noticeable. A good test
folder that's typically large for most users is  ~/.cache/thumbnails/large
where preview thumbnails are cached by the system, opening that should trigger
it if you have a lot of previews.

OBSERVED RESULT
The directory takes minutes to load as Dolphin is barely responsive during the
process.

EXPECTED RESULT
Over a month ago it would only take a few seconds, something clearly changed
affecting directory loading speeds on Dolphin or some KDE component
exclusively.

SOFTWARE/OS VERSIONS
Operating System: Manjaro Linux 
KDE Plasma Version: 5.27.9
KDE Frameworks Version: 5.111.0
Qt Version: 5.15.11
Kernel Version: 6.6.0-1-MANJARO (64-bit)
Graphics Platform: Wayland
Processors: 16 × AMD Ryzen 7 3700X 8-Core Processor
Memory: 31.3 GiB of RAM
Graphics Processor: AMD Radeon RX 570 Series

ADDITIONAL INFORMATION
Attached /etc/fstab as it's been previously pointed out Dolphin had issues with
certain parameters there. The affected partition is a SATA3 HDD, I'm also able
to reproduce it on my SSD where loading a large directory with lots of images
is abnormally slow as well... both are ext4. No drive errors, booted with
"fsck.mode=force fsck.repair=yes" to make extra sure and the issue persists
even afterward. Baloo is enabled but the affected directories are not indexed.
Enabling or disabling previews in Dolphin doesn't make any difference. Extra
discussion of the issue on the Manjaro Linux forum:

https://forum.manjaro.org/t/dolphin-loading-of-large-directories-very-slow-after-update/149727

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