Re: [RFC 0/13] extents and 48bit ext3

Jeff Garzik
2006-06-09T17:07:45Z

Andrew Morton wrote:
> On Fri, 09 Jun 2006 11:40:03 -0400
> Jeff Garzik <jeff@garzik.org> wrote:
>
>> Users are now forced to remember that, if they write to their filesystem
>> after using either $mmver or $korgver kernels, they are locked out of
>> using older kernels.
>
> The same happens if we create ext4 - earlier kernels don't support that,
> either.
>
> I suppose we could call it ext4, although that wouldn't make much
> difference operationally. The developers would probably choose to generate
> ext4 from the same codebase as ext3 for maintainability reasons, rather
> than choosing to copy-n-modify. We'd need to see the patches to be able to
> finally make that judgement.

I would propose the obvious... 'cp -a ext3 ext4', apply the extent and
48bit patches, and then do the obvious search-n-replace.

I guarantee that developer momentum would take over from there. Rather
than fundamentally change ext3, let's let it stabilize.

>> And as features continue to be added in this manner, this problem gets
>> _exponentially_ worse.
>
> "continue to be added"? afaik this is the first time this has happened,
> and there's no plan to do it again.

ext3 developers are _fundamentally changing_ the block allocation
structure [in a good way]. If they can get away with it once, they will
continue to modify ext3, adding btrees and other new gadgets. That's
just human nature. For example, htree was a minor disaster,
deployment-wise, on the distro vendor side.

I think extents and 48bit are so fundamental that it's silly to attempt
to minimize the impact from the user's perspective, and moreover, I
think Linux benefits more if ext3 is _not_ kept on life support this way.

We need to draw a line in the sand. If we don't, no one ever will.

Jeff