On Wed, Dec 12 2018 at 11:12am -0500, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > Does it really make sense to enhance dm-snapshot? I thought all serious > users of snapshots had moved on to dm-thinp? There are cases where dm-snapshot is still useful for people. But those are very niche users. I'm not opposed to others proposing enhancements for dm-snapshot in general but it is definitely not a priority (Google's dm-bow is an example of a case where dm-snapshot may get extended to fulfill google's needs). But for this specific DAX case, I can only assume efforts to prop up dm-snapshot like this are born out of legacy use-cases. The reality is getting DAX to work with dm-snapshot is pretty involved (due to mmap, etc). This thread got into a lot of the details: https://www.redhat.com/archives/dm-devel/2018-August/msg00211.html So any new attempt to reintroduce DAX support to dm-snapshot (or any more complex DM target) will have a very high bar. One that requires much more extensive mm and block (interlock) prep work to make DAX safe. Mike
