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:

quoted

On 2011年07月31日 15:08, Joel Becker Wrote:

quoted

On Sat, Jul 30, 2011 at 03:25:32PM +0800, Coly Li wrote:

quoted

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@evilplan.org
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