Add a pair of flags forcing fsync during copy loop
Review Request #130084 - Created April 12, 2017 and updated
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.
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.
But doesn't this make copying much slower in the normal case? (copying onto a non-removable harddisk partition).
It sounds to me like this should be
1) done internally in kio_file (no Job API for this)
2) only when the destination is a removable device
Removed the Job API changes; fsync is now always used when the target is on removeable media
Revision 2 (+137 -1)