linux-ext4 - Re: [PATCH 10/35] undo-io: add new calls to and speed up the undo io manager

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Message-ID: <20150505142025.GB12468@thunk.org>
Date:	Tue, 5 May 2015 10:20:25 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	"Darrick J. Wong" <darrick.wong@...cle.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 10/35] undo-io: add new calls to and speed up the undo io
 manager

On Wed, Apr 01, 2015 at 07:35:06PM -0700, Darrick J. Wong wrote:
> Implement pass-through calls for discard, zero-out, and readahead in
> the IO manager so that we can take advantage of any underlying
> support.
> 
> Furthermore, improve tdb write-out speed by disabling locking and only
> fsyncing at the end -- we don't care about locking because having
> multiple writers to the undo file will produce an undo database full
> of garbage blocks; and we only need to fsync at the end because if we
> fail before the end, our undo file will lack the necessary superblock
> data that e2undo requires to do replay safely.  Without this, we call
> fsync four times per tdb update(!)  This reduces the overhead of using
> undo_io while converting a 2TB FS to metadata_csum from 3+ hours to 55
> minutes.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>

Thanks, applied.

					- Ted
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