Messages in this thread | | | Date | Thu, 09 Mar 2006 16:45:50 -0800 | From | Badari Pulavarty <> | Subject | Re: [RFC PATCH] ext3 writepage() journal avoidance |
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Andrew Morton wrote:
>Badari Pulavarty <pbadari@us.ibm.com> wrote: > >>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). > Makes sense. I will take a look.
> >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'. >
Wow !! Never knew that. I assume we switch mapping->a_ops for this inode ?
>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. >
Sure. Thanks for your reply and valuable suggestions. :)
Thanks, Badari
>
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