Re: [PATCH 00/23] per device dirty throttling -v8

Andrew Morton
2007-08-05T06:00:07Z

On Sat, 04 Aug 2007 21:16:35 +0200 Florian Weimer <fw@deneb.enyo.de> wrote:

> * Andrew Morton:
>
> > The easy preventive is to mount with data=writeback. Maybe that should
> > have been the default.
>
> The documentation I could find suggests that this may lead to a
> security weakness (old data in blocks of a file that was grown just
> before the crash leaks to a different user).

yup. This problem also exists in ext2, reiserfs (unless using
ordered-mode), JFS, others.

> XFS overwrites that data
> with zeros upon reboot, which tends to irritate users when it happens.

yup.

> >From this point of view, data=ordered doesn't seem too bad.

If your computer is used by multiple users who don't trust each other,
sure. That covers, what? About 2% of machines?

I was using data=writeback for a while on my most-thrashed disk. The
results were a bit disappointing - not much difference. ext2 is a lot
quicker.

(I don't use anything which is fsync-happy, btw). (I used to have a patch
which sysctl-tunably turned fsync, msync, fdatasync into "return 0" for use
on the laptop but I seem to have lost it)