On Wed 24-05-17 17:27:36, Mike Rapoport wrote:

On Wed, May 24, 2017 at 01:18:00PM +0200, Michal Hocko wrote:

[...]

quoted

Why cannot khugepaged simply skip over all VMAs which have userfault
regions registered? This would sound like a less error prone approach to
me.

khugepaged does skip over VMAs which have userfault. We could register the
regions with userfault before populating them to avoid collapses in the
transition period.

Why cannot you register only post-copy regions and "manually" copy the
pre-copy parts?

But then we'll have to populate these regions with
UFFDIO_COPY which adds quite an overhead.

How big is the performance impact?
-- 
Michal Hocko
SUSE Labs