Messages in this thread | | | Date | Thu, 5 Jan 2023 16:29:41 +0100 | Subject | Re: [PATCH 09/46] mm: add MADV_SPLIT to enable HugeTLB HGM | From | David Hildenbrand <> |
| |
On 05.01.23 11:18, James Houghton wrote: > Issuing ioctl(MADV_SPLIT) on a HugeTLB address range will enable > HugeTLB HGM. MADV_SPLIT was chosen for the name so that this API can be > applied to non-HugeTLB memory in the future, if such an application is > to arise. > > MADV_SPLIT provides several API changes for some syscalls on HugeTLB > address ranges: > 1. UFFDIO_CONTINUE is allowed for MAP_SHARED VMAs at PAGE_SIZE > alignment. > 2. read()ing a page fault event from a userfaultfd will yield a > PAGE_SIZE-rounded address, instead of a huge-page-size-rounded > address (unless UFFD_FEATURE_EXACT_ADDRESS is used). > > There is no way to disable the API changes that come with issuing > MADV_SPLIT. MADV_COLLAPSE can be used to collapse high-granularity page > table mappings that come from the extended functionality that comes with > using MADV_SPLIT. > > For post-copy live migration, the expected use-case is: > 1. mmap(MAP_SHARED, some_fd) primary mapping > 2. mmap(MAP_SHARED, some_fd) alias mapping > 3. MADV_SPLIT the primary mapping > 4. UFFDIO_REGISTER/etc. the primary mapping > 5. Copy memory contents into alias mapping and UFFDIO_CONTINUE the > corresponding PAGE_SIZE sections in the primary mapping. > > More API changes may be added in the future. > > Signed-off-by: James Houghton <jthoughton@google.com> > --- > arch/alpha/include/uapi/asm/mman.h | 2 ++ > arch/mips/include/uapi/asm/mman.h | 2 ++ > arch/parisc/include/uapi/asm/mman.h | 2 ++ > arch/xtensa/include/uapi/asm/mman.h | 2 ++ > include/linux/hugetlb.h | 2 ++ > include/uapi/asm-generic/mman-common.h | 2 ++ > mm/hugetlb.c | 3 +-- > mm/madvise.c | 26 ++++++++++++++++++++++++++ > 8 files changed, 39 insertions(+), 2 deletions(-) > > diff --git a/arch/alpha/include/uapi/asm/mman.h b/arch/alpha/include/uapi/asm/mman.h > index 763929e814e9..7a26f3648b90 100644 > --- a/arch/alpha/include/uapi/asm/mman.h > +++ b/arch/alpha/include/uapi/asm/mman.h > @@ -78,6 +78,8 @@ > > #define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */ > > +#define MADV_SPLIT 26 /* Enable hugepage high-granularity APIs */
I think we should make a split more generic, such that it also splits (pte-maps) a THP. Has that been discussed?
-- Thanks,
David / dhildenb
| |