On Wed, Nov 16, 2022 at 2:28 PM Peter Xu <peterx@xxxxxxxxxx> wrote: > > On Fri, Oct 21, 2022 at 04:36:49PM +0000, James Houghton wrote: > > Userspace must provide this new feature when it calls UFFDIO_API to > > enable HGM. Userspace can check if the feature exists in > > uffdio_api.features, and if it does not exist, the kernel does not > > support and therefore did not enable HGM. > > > > Signed-off-by: James Houghton <jthoughton@xxxxxxxxxx> > > It's still slightly a pity that this can only be enabled by an uffd context > plus a minor fault, so generic hugetlb users cannot directly leverage this. The idea here is that, for applications that can conceivably benefit from HGM, we have a mechanism for enabling it for that application. So this patch creates that mechanism for userfaultfd/UFFDIO_CONTINUE. I prefer this approach over something more general like MADV_ENABLE_HGM or something. For hwpoison, HGM will be automatically enabled, but that isn't implemented in this series. We could also extend MADV_DONTNEED to do high-granularity unmapping in some way, but that also isn't attempted here. I'm sure that if there are other cases where HGM may be useful, we can add/change some uapi to make it possible to take advantage HGM. - James > > The patch itself looks good. > > -- > Peter Xu >
