Badari Pulavarty <pbadari@xxxxxxxxxx> wrote:Makes sense. I will take a look.
I am trying to speed up ext3 writepage() by avoiding
journaling in non-block allocation cases. Does this
look reasonable ? So far, my testing is fine. What am I missing here ?
Nothing. ext3's writepage(), prepare_write() and commit_write() do often
needlessy open and close transactions when we're doing overwrites. It's
something I've meant to look at for a few years, on and off.
I'd expect that prepare_write() and commit_write() are more important than
writepage().
It might be better to test PageMappedToDisk() rather than walking the
buffers. It's certainly faster and it makes optimisation of
prepare_write() and commit_write() easier to handle.
I'm not sure that PageMappedToDisk() gets set in all the right places
though - it's mainly for the `nobh' handling and block_prepare_write()
would need to be taught to set it. I guess that'd be a net win, even if
only ext3 uses it..
Then again, we might be able to speed up block_prepare_write() if
PageMappedToDisk(page).
If we go this way we need to be very very careful to keep PG_mappedtodisk
coherent with the state of the buffers. Tricky. We need to think about
whether block_truncate_page() should be clearing PG_mappedtoisk if we did a
partial truncate.
Don't forget that ext3 supports journalled-mode files on ordered- or
writeback-mounted filesystems, via `chattr +j'.
Please be sure to test the
various combinations which that allows when playing with the write paths -
it can trip things up.
Also be sure to test nobh-mode.