lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  linux-cve-announce  PHC 
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:	Mon, 30 Apr 2012 10:51:43 -0600
From:	Andreas Dilger <>
Cc:	"Ted Ts'o" <>,
	Sunil Mushran <>,
	Martin K Petersen <>,
	Greg Freemyer <>,
	Amir Goldstein <>,
	linux-kernel <>,
	Andi Kleen <>,
	Mingming Cao <>,
	Joel Becker <>,
	linux-fsdevel <>,, Coly Li <>
Subject: Re: [PATCH 15/23] jbd2: Change disk layout for metadata checksumming

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

To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to
More majordomo info at

Powered by blists - more mailing lists