Every close of a dirty cache item re-adds it to the writeback queue,
and WriteBack.Add reset the upload timer even when the file had not
been modified since it was last queued. A file which is opened and
closed more often than --vfs-write-back - for example a git object
that another process keeps reading - therefore never got uploaded
while the reads continued.
Before this change, with --vfs-write-back 2s, a file reread every
0.5s through a mount was still not uploaded after 12s of reads. After
it the file is uploaded after 2.6s, while the reads carry on.
This only moves the timer on when the item has been modified, which
was already the condition for cancelling an upload in progress. An
unmodified re-add now also leaves the retry backoff of a failed
upload alone.
Neil Cawse
d1c54c4e5d