Re: JFYI: ext4 bug triggerable by kvm

Anthony Liguori
2010-08-17T14:44:55Z

On 08/17/2010 09:40 AM, Michael Tokarev wrote:
>
>>> fsync() being slow is orthogonal to my point. I don't see why we
>>> need to do an fsync() on *every* write. It should only be necessary
>>> when a guest injects an actual barrier.
>>>
> We don't do sync on every write, but O_SYNC implies that.
> And apparently it is what happening behind the scenes in
> ext4 O_SYNC case.
>

I think the real issue is we're mixing host configuration with guest
visible state.

With O_SYNC, we're causing cache=writethrough to do writethrough through
two layers of the storage heirarchy. I don't think that's necessary or
desirable though.

Regards,

Anthony Liguori

> But ok....
>
> /mjt
>