Re: [PATCH 1/2] ext4: Calculate and verify inode checksums
From: Sunil Mushran
Date: Thu Apr 07 2011 - 13:11:16 EST
On 04/07/2011 09:40 AM, Darrick J. Wong wrote:
Yes, I see that jbd2 has triggers, looks like a nifty feature. I suppose if I
went with that approach I'd still have to calculate the checksum in
ext4_do_update_inode in the nojournal case, and in the journal case I'd write a
trigger that would figure out which inodes in a given buffer are actually dirty
and compute their checksums.
Yes, you could use a in-mem flag (set in update, cleared in trigger) to
identify dirty inodes. The discussion on stable pages could be relevant for
the nojournal case.
That said, I haven't really quantified the performance impact of this naive
approach yet, so I wonder -- did you see a similar scenario with ocfs2, and
what kind of performance increase did you get by adapting the code to use the
jbd2 trigger? If there's potentially a large increase, it would be interesting
to apply the same conversion to the group descriptor checksumming code too.
Joel Becker may remember the overhead. He wrote the patch. That said we have few
differences. ocfs2 has larger (blocksized) inodes. Also, it computes ECC. The code
is in fs/ocfs2/blockcheck.c.
As in, you may want to generate ext4 specific numbers.
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