On Thu, 2006-03-16 at 16:04 -0500, Theodore Ts'o wrote:
> On Thu, Mar 16, 2006 at 10:22:40AM -0800, Badari Pulavarty wrote:
> > > However, if what we are doing is overwriting our own data with more an
> > > updated, more recent version of the data block, do we guarantee that
> > > any ordering semantics apply? For example, what if we write a data
> > > block, and then follow it up with some kind of metadata update (say we
> > > touch atime, or add an extended attribute). Do we guarantee that if
> > > the metadata update is committed, that the data block will have made
> > > it to disk as well?
> >
> > I don't see how we do this today. Yes. Metadata updates are jounalled,
> > but I don't see how current adding buffers through journal_dirty_data
> > (bh) call can guarantee that these buffers get added to metadata-update
> > transaction ?
>
> Even though there aren't any updates to any metadata blocks that take
> place between the journal_start() and journal_stop() calls, if
> journal_dirty_data() is called (for example in ordered_writepage),
> those buffers will be associated with the currently open transaction,
> so they will be guaranteed to be written before the transaction is
> allowed to commit.
>
> Remember, journal_start and journal_stop do not delineate a full
> ext3/jbd transaction, but rather an operation, where a large number of
> operations are bundled together to form a transaction. When you call
> journal_start, and request a certain number of credits (number of
> buffers that you maximally intend to dirty), that opens up an
> operation. If the operation turns out not to dirty any metadata
> blocks at the time of journal_stop(), all of the credits that were
> reserved by jouranl_start() are returned to the currently open
> transaction. However, any data blocks which are marked via
> journal_dirty_data() are still going to be associated with the
> currently open transaction, and they will still be forced out before
> the transaction is allowed to commit.
>
> Does that make sense?
Makes perfect sense, except that it doesn't match what I see through
"debugfs" - logdump :(
I wrote a testcase to re-write same blocks again & again - there is
absolutely nothing showed up in log. Which implied to me that, all
the jorunal_dirty_data we did on all those buffers, did nothing -
since there is no current transaction. What am I missing ?
Thanks,
Badari
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
