>Well, you are pretty much on your own, then. Really, we cannot help
>diagnose problems on old kernels with a random set of backported
>patches in them.
Definitely understood. I just wanted to ask that original
question, really. I had assumed that the file system itself
had to start any dirty-page writes, having missed the top level
filemap_fdatawrite() call.
We finally got a test case and did a bunch of analysis, and it
turns out that the DB software is missing an fsync() call. Of
course XFS won't fsync the file if you don't *ask* it to!
As long as I am sending mail, there is something else I am curious
about though. While this is not XFS specific, I wonder if there
is any desire to have different background write frequencies on
different file systems. By default, mm/page-writeback.c will start
writebacks after a 30-second delay. One can tune this to any other
number (via /proc/sys/vm/dirty_{expire,writeback}_centisecs), but
this affects the entire system. It might be useful to be able
to tune this per-FS instead.
(On the other hand, perhaps if one really wants one's data journaled,
one should just use a data-journaling file system....)
Chris
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