On Wed, Feb 22, 2023 at 7:49 AM David Hildenbrand <david@xxxxxxxxxx> wrote: > > On 21.02.23 22:46, Mike Kravetz wrote: > > On 02/18/23 00:27, James Houghton wrote: > >> This series introduces the concept of HugeTLB high-granularity mapping > >> (HGM). This series teaches HugeTLB how to map HugeTLB pages at > >> high-granularity, similar to how THPs can be PTE-mapped. > >> > >> Support for HGM in this series is for MAP_SHARED VMAs on x86_64 only. Other > >> architectures and (some) support for MAP_PRIVATE will come later. > >> > >> This series is based on latest mm-unstable (ccd6a73daba9). > >> > >> Notable changes with this series > >> ================================ > >> > >> - hugetlb_add_file_rmap / hugetlb_remove_rmap are added to handle > >> mapcounting for non-anon hugetlb. > >> - The mapcounting scheme uses subpages' mapcounts for high-granularity > >> mappings, but it does not use subpages_mapcount(). This scheme > >> prevents the HugeTLB VMEMMAP optimization from being used, so it > >> will be improved in a later series. > >> - page_add_file_rmap and page_remove_rmap are updated so they can be > >> used by hugetlb_add_file_rmap / hugetlb_remove_rmap. > >> - MADV_SPLIT has been added to enable the userspace API changes that > >> HGM allows for: high-granularity UFFDIO_CONTINUE (and maybe other > >> changes in the future). MADV_SPLIT does NOT force all the mappings to > >> be PAGE_SIZE. > >> - MADV_COLLAPSE is expanded to include HugeTLB mappings. > >> > >> Old versions: > >> v1: https://lore.kernel.org/linux-mm/20230105101844.1893104-1-jthoughton@xxxxxxxxxx/ > >> RFC v2: https://lore.kernel.org/linux-mm/20221021163703.3218176-1-jthoughton@xxxxxxxxxx/ > >> RFC v1: https://lore.kernel.org/linux-mm/20220624173656.2033256-1-jthoughton@xxxxxxxxxx/ > >> > >> Changelog: > >> v1 -> v2 (thanks Peter for all your suggestions!): > >> - Changed mapcount to be more THP-like, and make HGM incompatible with > >> HVO. > >> - HGM is now disabled by default to leave HVO enabled by default. > > > > I understand the reasoning behind the move to THP-like mapcounting, and the > > incompatibility with HVO. However, I just got to patch 5 and realized either > > HGM or HVO will need to be chosen at kernel build time. That may not be an > > issue for cloud providers or others building their own kernels for internal > > use. However, distro kernels will need to pick one option or the other. > > Right now, my Fedora desktop has HVO enabled so it would likely not have > > HGM enabled. That is not a big deal for a desktop. > > > > Just curious, do we have distro kernel users that want to use HGM? > > Most certainly I would say :) > Is it a blocker to merge in an initial implementation though? Do distro kernel users have a pressing need for HVO + HGM used in tandem? > -- > Thanks, > > David / dhildenb >
