Andrew Morton wrote:
Badari Pulavarty <[email protected]> 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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