Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE

[Michal Hocko]

On Wed 24-05-17 17:27:36, Mike Rapoport wrote:
> On Wed, May 24, 2017 at 01:18:00PM +0200, Michal Hocko wrote:
[...]
> > 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