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>
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 */
+
/* compatibility flags */
#define MAP_FILE 0
diff --git a/arch/mips/include/uapi/asm/mman.h b/arch/mips/include/uapi/asm/mman.h
index c6e1fc77c996..f8a74a3a0928 100644
--- a/arch/mips/include/uapi/asm/mman.h
+++ b/arch/mips/include/uapi/asm/mman.h
@@ -105,6 +105,8 @@
#define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */
+#define MADV_SPLIT 26 /* Enable hugepage high-granularity APIs */
+
/* compatibility flags */
#define MAP_FILE 0
diff --git a/arch/parisc/include/uapi/asm/mman.h b/arch/parisc/include/uapi/asm/mman.h
index 68c44f99bc93..a6dc6a56c941 100644
--- a/arch/parisc/include/uapi/asm/mman.h
+++ b/arch/parisc/include/uapi/asm/mman.h
@@ -72,6 +72,8 @@
#define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */
+#define MADV_SPLIT 74 /* Enable hugepage high-granularity APIs */
+
#define MADV_HWPOISON 100 /* poison a page for testing */
#define MADV_SOFT_OFFLINE 101 /* soft offline page for testing */
diff --git a/arch/xtensa/include/uapi/asm/mman.h b/arch/xtensa/include/uapi/asm/mman.h
index 1ff0c858544f..f98a77c430a9 100644
--- a/arch/xtensa/include/uapi/asm/mman.h
+++ b/arch/xtensa/include/uapi/asm/mman.h
@@ -113,6 +113,8 @@
#define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */
+#define MADV_SPLIT 26 /* Enable hugepage high-granularity APIs */
+
/* compatibility flags */
#define MAP_FILE 0
diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h
index 6ce1f1ceb432..996e8ded092f 100644
--- a/include/uapi/asm-generic/mman-common.h
+++ b/include/uapi/asm-generic/mman-common.h
@@ -79,6 +79,8 @@
#define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */
+#define MADV_SPLIT 26 /* Enable hugepage high-granularity APIs */
+
/* compatibility flags */
#define MAP_FILE 0
diff --git a/mm/madvise.c b/mm/madvise.c
index c2202f51e9dd..8c004c678262 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -1006,6 +1006,28 @@ static long madvise_remove(struct vm_area_struct *vma,
return error;
}
+static int madvise_split(struct vm_area_struct *vma,
+ unsigned long *new_flags)
+{
+#ifdef CONFIG_HUGETLB_HIGH_GRANULARITY_MAPPING
+ if (!is_vm_hugetlb_page(vma) || !hugetlb_hgm_eligible(vma))
+ return -EINVAL;
+
+ /*
+ * PMD sharing doesn't work with HGM. If this MADV_SPLIT is on part
+ * of a VMA, then we will split the VMA. Here, we're unsharing before
+ * splitting because it's simpler, although we may be unsharing more
+ * than we need.
+ */
+ hugetlb_unshare_all_pmds(vma);
+
+ *new_flags |= VM_HUGETLB_HGM;
+ return 0;
+#else
+ return -EINVAL;
+#endif
+}
+
/*
* Apply an madvise behavior to a region of a vma. madvise_update_vma
* will handle splitting a vm area into separate areas, each area with its own
@@ -1084,6 +1106,11 @@ static int madvise_vma_behavior(struct vm_area_struct *vma,
break;
case MADV_COLLAPSE:
return madvise_collapse(vma, prev, start, end);
+ case MADV_SPLIT:
+ error = madvise_split(vma, &new_flags);
+ if (error)
+ goto out;
+ break;
}
anon_name = anon_vma_name(vma);
@@ -1178,6 +1205,9 @@ madvise_behavior_valid(int behavior)
case MADV_HUGEPAGE:
case MADV_NOHUGEPAGE:
case MADV_COLLAPSE:
+#endif
+#ifdef CONFIG_HUGETLB_HIGH_GRANULARITY_MAPPING
+ case MADV_SPLIT:
#endif
case MADV_DONTDUMP:
case MADV_DODUMP:
@@ -1368,6 +1398,8 @@ int madvise_set_anon_name(struct mm_struct *mm, unsigned long start,
* transparent huge pages so the existing pages will not be
* coalesced into THP and new pages will not be allocated as THP.
* MADV_COLLAPSE - synchronously coalesce pages into new THP.
+ * MADV_SPLIT - allow HugeTLB pages to be mapped at PAGE_SIZE. This allows
+ * UFFDIO_CONTINUE to accept PAGE_SIZE-aligned regions.
* MADV_DONTDUMP - the application wants to prevent pages in the given range
* from being included in its core dump.
* MADV_DODUMP - cancel MADV_DONTDUMP: no longer exclude from core dump.
--
2.39.2.637.g21b0678d19-goog
