Vishal Annapurve wrote: > On Fri, Jul 11, 2025 at 3:56 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote: > > > > On Fri, Jul 11, 2025, Ira Weiny wrote: > > > Michael Roth wrote: > > > > For in-place conversion: the idea is that userspace will convert > > > > private->shared to update in-place, then immediately convert back > > > > shared->private; > > > > > > Why convert from private to shared and back to private? Userspace which > > > knows about mmap and supports it should create shared pages, mmap, write > > > data, then convert to private. > > > > Dunno if there's a strong usecase for converting to shared *and* populating the > > data, but I also don't know that it's worth going out of our way to prevent such > > behavior, at least not without a strong reason to do so. E.g. if it allowed for > > a cleaner implementation or better semantics, then by all means. But I don't > > think that's true here? Though I haven't thought hard about this, so don't > > quote me on that. :-) > > If this is a huge page backing, starting as shared will split all the > pages to 4K granularity upon allocation. Why? What is the reason it needs to be split? > To avoid splitting, userspace > can start with everything as private when working with hugepages and > then follow convert to shared -> populate -> convert to private as > needed. I'm not saying this could not be done but seems wasteful. Ira
