Messages in this thread | | | Date | Thu, 09 Mar 2006 16:36:53 -0800 | From | Badari Pulavarty <> | Subject | Re: ext3_ordered_writepage() questions |
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Andrew Morton wrote:
>Badari Pulavarty <pbadari@us.ibm.com> wrote: > >>Hi, >> >>I am trying to cleanup ext3_ordered and ext3_writeback_writepage() routines. >>I am confused on what ext3_ordered_writepage() is currently doing ? I hope >>you can help me understand it little better. >> >>1) Why do we do journal_start() all the time ? >> > >Because we're lame. > >>2) Why do we call journal_dirty_data_fn() on the buffers ? We already >>issued IO on all those buffers() in block_full_write_page(). Why do we >>need to add them to transaction ? I understand we need to do this for >>block allocation case. But do we need it for non-allocation case also ? >> > >Yup. Ordered-mode JBD commit needs to write and wait upon all dirty >file-data buffers prior to journalling the metadata. If we didn't run >journal_dirty_data_fn() against those buffers then they'd still be under >I/O after commit had completed. > In non-block allocation case, what metadata are we journaling in writepage() ? block allocation happend in prepare_write() and commit_write() journaled the transaction. All the meta data updates should be done there. What JBD commit are you refering to here ?
> >But I think if you're looking for CPU consumption reductions, you'd be much >better off attacking prepare_write() and commit_write(), rather than >writepage(). >
Yes. You are right. I never realized that, we call prepare_write()/commit_write() for each write. I was under the impression that we do it only on the first instantiation of the page. I will take a closer look at it.
The reasons for looking at writepage() are:
- want to support writepages() for ext3. Last time when I tried, ran into page->lock and journal_start() deadlock. Thats why I want to understand the journalling better and clean it up while looking at it.
- eventually, I want to add delayed allocation to make use of multiblock allocation. Right now, we can't make use of multiblock allocation for buffered mode :(
Thanks, Badari
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