On Tue, May 30, 2017 at 09:44:08AM +0200, Michal Hocko wrote: > 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? We can register only post-copy regions, but this will cause VMA fragmentation. Now we register the entire VMA with userfaultfd, no matter how many pages were dirtied there since the pre-dump. If we register only post-copy regions, we will split out the VMAs for those regions. > > But then we'll have to populate these regions with > > UFFDIO_COPY which adds quite an overhead. > > How big is the performance impact? I don't have the numbers handy, but for each post-copy range it means that instead of memcpy() we will use ioctl(UFFDIO_COPY). > -- > Michal Hocko > SUSE Labs -- Sincerely yours, Mike. -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
