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@xxxxxxxxxx>
---
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
