On Sun, Jul 31, 2011 at 09:57:11PM -0700, Joel Becker wrote:
> On Mon, Aug 01, 2011 at 07:52:41AM +0800, Coly Li wrote:
> > On 2011年07月31日 15:08, Joel Becker Wrote:
> > > On Sat, Jul 30, 2011 at 03:25:32PM +0800, Coly Li wrote:
> > >> And in non-journal mode, there is not copy of any meta data block in jbd2, we need to be
> > >> more careful in check summing, e.g. inode/block bitmap blocks...
> > >
> > > Sure, but you could use a trigger in journaled mode and then do
> > > the checksums directly in the __ext4_handle_journal_dirty_*() functions
> > > in non-journaled mode. Sure, it would be a little more CPU time, but
> > > the user picked "checksums + no journal" at mkfs time.
> > >
> >
> > Yes, my idea was similar to you.
> > One thing not clear to me is, in non-journal mode, how to make the page of bitmap block being stable. Because bits
> > setting in Ext4 bitmap is non-locking, it might be possible that new bit setting after check sum is calculated.
>
> Every place that changes the bits will eventually call
> ext4_journal_dirty(), which recalculates the checksum. So there's no
> danger of a set-bit-after-last-checksum. But you will have to lock
> around the checksum calculation in non-journaling mode. JBD2 handles it
> for journaling mode.
Wait, bitsetting in ext4 can't be non-locking. Or are they
crazily stomping on memory? I sure see an assert_spin_locked() in
mb_mark_used().
Joel
--
"Well-timed silence hath more eloquence than speech."
- Martin Fraquhar Tupper
http://www.jlbec.org/
jlbec@xxxxxxxxxxxx
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
