From: Andreas Dilger <adilger.kernel@dilger.ca>
To: djwong@us.ibm.com
Cc: "Ted Ts'o" <tytso@mit.edu>,
Sunil Mushran <sunil.mushran@oracle.com>,
Martin K Petersen <martin.petersen@oracle.com>,
Greg Freemyer <greg.freemyer@gmail.com>,
Amir Goldstein <amir73il@gmail.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
Andi Kleen <andi@firstfloor.org>, Mingming Cao <cmm@us.ibm.com>,
Joel Becker <jlbec@evilplan.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
linux-ext4@vger.kernel.org, Coly Li <colyli@gmail.com>
Subject: Re: [PATCH 15/23] jbd2: Change disk layout for metadata checksumming
Date: Mon, 30 Apr 2012 10:51:43 -0600 [thread overview]
Message-ID: <29C40967-4A9E-4D32-B356-A5D15E23EB38@dilger.ca> (raw)
In-Reply-To: <20120430155341.GC6938@tux1.beaverton.ibm.com>
On 2012-04-30, at 9:53 AM, djwong wrote:
> As for putting half the checksum into the upper 16 bits of the flags
> field -- is journal space at such a premium that we need to overload
> the field and reduce the strength of the checksum? Enabling journal
> checksums on a 4k block filesystem causes tags_per_block to decrease
> from 512 to 341 on a 32bit journal and from 341 to 256 on a 64bit
> journal. Do transactions typically have that many blocks? I didn't
> think most transactions had 1-2MB of dirty data.
I think on a busy filesystem there can be many thousands of blocks in
a single transaction. We run Lustre with 400MB journals, and under
metadata-intensive workloads we can hit the 100MB transaction size
limit easily. However, this doesn't mean there are 25k blocks in
each transaction, since most of these blocks are reserved for the
worst case, but not used.
As for the impact of reducing the number of tags in each block, for a
4096-block transaction this would currently mean 8 32-bit tag blocks,
and it would grow to 12 or 13, which isn't significant in the end.
My suggestion was mostly to avoid problems with the disk format change.
If this can be handled in another manner, AND it doesn't break journal
recovery on older kernels/e2fsprogs, then I'm OK with the cleaner
approach. Please ensure that this is tested.
Cheers, Andreas
next prev parent reply other threads:[~2012-04-30 16:51 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-03-06 20:47 [PATCH v3 00/23] ext4: Add metadata checksumming Darrick J. Wong
2012-03-06 20:48 ` [PATCH 01/23] ext4: Create a new BH_Verified flag to avoid unnecessary metadata validation Darrick J. Wong
2012-03-06 20:48 ` [PATCH 02/23] ext4: Change on-disk layout to support extended metadata checksumming Darrick J. Wong
2012-03-06 20:48 ` [PATCH 03/23] ext4: Record the checksum algorithm in use in the superblock Darrick J. Wong
2012-03-06 20:48 ` [PATCH 04/23] ext4: Only call out to crc32c if necessary Darrick J. Wong
2012-03-06 20:48 ` [PATCH 05/23] ext4: Calculate and verify superblock checksum Darrick J. Wong
2012-04-27 20:05 ` Ted Ts'o
2012-04-30 16:19 ` djwong
2012-03-06 20:48 ` [PATCH 06/23] ext4: Calculate and verify inode checksums Darrick J. Wong
2012-03-06 20:48 ` [PATCH 07/23] ext4: Calculate and verify checksums for inode bitmaps Darrick J. Wong
2012-03-06 20:48 ` [PATCH 08/23] ext4: Calculate and verify block bitmap checksum Darrick J. Wong
2012-03-06 20:48 ` [PATCH 09/23] ext4: Verify and calculate checksums for extent tree blocks Darrick J. Wong
2012-03-06 20:49 ` [PATCH 10/23] ext4: Calculate and verify checksums for htree nodes Darrick J. Wong
2012-03-06 20:49 ` [PATCH 11/23] ext4: Calculate and verify checksums of directory leaf blocks Darrick J. Wong
2012-03-06 20:49 ` [PATCH 12/23] ext4: Calculate and verify checksums of extended attribute blocks Darrick J. Wong
2012-03-06 20:49 ` [PATCH 13/23] ext4: Make block group checksums use metadata_csum algorithm Darrick J. Wong
2012-03-06 20:49 ` [PATCH 14/23] ext4: Add checksums to the MMP block Darrick J. Wong
2012-03-06 20:49 ` [PATCH 15/23] jbd2: Change disk layout for metadata checksumming Darrick J. Wong
2012-04-28 14:19 ` Ted Ts'o
2012-04-28 22:58 ` Andreas Dilger
2012-04-30 15:53 ` djwong
2012-04-30 16:51 ` Andreas Dilger [this message]
2012-03-06 20:49 ` [PATCH 16/23] jbd2: Enable journal clients to enable v2 checksumming Darrick J. Wong
2012-03-06 20:49 ` [PATCH 17/23] jbd2: Grab a reference to the crc32c driver only when necessary Darrick J. Wong
2012-03-06 20:50 ` [PATCH 18/23] jbd2: Checksum journal superblock Darrick J. Wong
2012-03-06 20:50 ` [PATCH 19/23] jbd2: Checksum revocation blocks Darrick J. Wong
2012-03-06 20:50 ` [PATCH 20/23] jbd2: Checksum descriptor blocks Darrick J. Wong
2012-03-06 20:50 ` [PATCH 21/23] jbd2: Checksum commit blocks Darrick J. Wong
2012-03-06 20:50 ` [PATCH 22/23] jbd2: Checksum data blocks that are stored in the journal Darrick J. Wong
2012-03-06 20:50 ` [PATCH 23/23] ext4/jbd2: Add metadata checksumming to the list of supported features Darrick J. Wong
-- strict thread matches above, loose matches on Subject: below --
2012-01-07 8:27 [PATCH v2.3 00/23] ext4: Add metadata checksumming Darrick J. Wong
2012-01-07 8:29 ` [PATCH 15/23] jbd2: Change disk layout for " Darrick J. Wong
2011-12-14 0:46 [PATCH v2.2 00/23] ext4: Add " Darrick J. Wong
2011-12-14 0:47 ` [PATCH 15/23] jbd2: Change disk layout for " Darrick J. Wong
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