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https://git.reviewboard.kde.org/r/130084/
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Review request for KDE Frameworks.


Repository: kio


Description
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When copying a large-ish file (~1-2GB) from very fast storage to very slow 
storage (e.g. an NVME SSD to a cheap USB flash drive) on a machine with lots of 
RAM, Dolphin displays a progress bar which finishes in a fraction of a second 
(i.e. as fast as it takes to read the source file into the Linux page cache). 
Unmounting the drive then of course takes a long time, with only an 
indeterminate spinner.

This patch adds an option to force fsync during copy jobs, so that the copy 
progress bar measures how long it will take to actually copy the file to the 
destination.

I've added two flags - Fsync and FsyncCrossFilesystem - to the JobEnum flag. 
The former will cause all copy operations to fsync during the copy loop, whilst 
the latter will only fsync copies that are across different filesystems.

If this patch gets OK'd, I have another patch which adds support for this into 
the appropriate places in Dolphin. I would think that at least 
FsyncCrossFilesystem should be the default, but Fsync always might be a little 
heavy handed. At the least fsync'ing cross-filesystem copies ensures that the 
unmount won't take forever.


Diffs
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Diff: https://git.reviewboard.kde.org/r/130084/diff/


Testing
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Tested the patch with KDE/Dolphin on Arch Linux, which is version 5.32.0. The 
diff applies cleanly to master so I assume there shouldn't be any issues there, 
but I've not actually checked that. As advertised, copying a file to USB flash 
storage now displays an accurate progress bar.

I experimented with how often fsync should be called on my hardware, and I 
found calling it every ~1M copied caused no decrease in copy performance whilst 
still providing accurate progress info. That is the setting I've gone with in 
this patch. I'm open to suggestions on how this could be tuned better though.


Thanks,

KJ Tsanaktsidis

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