Re: WARNING in __mmdrop

On 2019/7/23 下午6:42, Michael S. Tsirkin wrote:

On Tue, Jul 23, 2019 at 04:42:19PM +0800, Jason Wang wrote:

quoted

quoted

So how about this: do exactly what you propose but as a 2 patch series:
start with the slow safe patch, and add then return uaddr optimizations
on top. We can then more easily reason about whether they are safe.

If you stick, I can do this.

So I definitely don't insist but I'd like us to get back to where
we know existing code is very safe (if not super fast) and
optimizing from there.  Bugs happen but I'd like to see a bisect
giving us "oh it's because of XYZ optimization" and not the
general "it's somewhere within this driver" that we are getting
now.

Syzbot has bisected to the commit of metadata acceleration in fact :)

Maybe the way to do this is to revert for this release cycle
and target the next one. What do you think?

I would try to fix the issues consider packed virtqueue which may use 
this for a good performance number. But if you insist, I'm ok to revert. 
Or maybe introduce a config option to disable it by default (almost all 
optimized could be ruled out).

Thanks


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