Re: Linux 2.6.29

Jeff Garzik
2009-03-29T04:54:18Z

Theodore Tso wrote:
> So having some mode where we can suspend all writes to the disk for up
> to a user-defined limit --- and then once the disk wakes up, for
> reading or for writing, we flush out all dirty data --- makes a lot of
> sense. Laptop mode does most of this already, except that it doesn't
> intercept fsync() requests. And as long as the user has given
> permission to the operating system to defer fsync() requests by up to
> some user-specified time limit, IMHO that's completely fair game.

Overall I agree, but I would rewrite that as: it's fair game as long as
the OS doesn't undercut the deliberate write ordering performed by the
userland application.

When the "laptop mode fsync plug" is uncorked, writes should not be
merged across an fsync(2) barrier; otherwise it becomes impossible to
build transactional databases with any consistency guarantees at all.

Jeff