MADV_SPLIT enables doublemap on hugetlb. Do that if doublemap=true
specified for the migration.
Signed-off-by: Peter Xu <pet...@redhat.com>
---
migration/postcopy-ram.c | 16 ++++++++++++++++
migration/ram.c | 18 ++++++++++++++++++
2 files changed, 34 insertions(+)
diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
index 86ff73c2c0..dbc7e54e4a 100644
--- a/migration/postcopy-ram.c
+++ b/migration/postcopy-ram.c
@@ -694,6 +694,22 @@ static int ram_block_enable_notify(RAMBlock *rb, void
*opaque)
*/
reg_struct.mode = UFFDIO_REGISTER_MODE_MISSING;
if (minor_fault) {
+ /*
+ * MADV_SPLIT implicitly enables doublemap mode for hugetlb. If
+ * that fails (e.g. on old kernels) we need to fail the migration.
+ *
+ * It's a bit late to fail here as we could have migrated lots of
+ * pages in precopy, but early failure will require us to allocate
+ * hugetlb pages secretly in QEMU which is not friendly to admins
+ * and it may affect the global hugetlb pool. Considering it is
+ * normally always limited, keep the failure late but tolerable.
+ */
+ if (qemu_madvise(qemu_ram_get_host_addr(rb), rb->postcopy_length,
+ QEMU_MADV_SPLIT)) {
+ error_report("%s: madvise(MADV_SPLIT) failed (ret=%d) but "
+ "required for doublemap.", __func__, -errno);
+ return -1;
+ }
reg_struct.mode |= UFFDIO_REGISTER_MODE_MINOR;
}
diff --git a/migration/ram.c b/migration/ram.c
index 37d7b3553a..4d786f4b97 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -3891,6 +3891,19 @@ static int migrate_hugetlb_doublemap_init(void)
RAMBLOCK_FOREACH_NOT_IGNORED(rb) {
if (qemu_ram_is_hugetlb(rb)) {
+ /*
+ * MADV_SPLIT implicitly enables doublemap mode for hugetlb on
+ * the guest mapped ranges. If that fails (e.g. on old
+ * kernels) we need to fail the migration. Note, the
+ * host_mirror mapping below can be kept as hugely mapped.
+ */
+ if (qemu_madvise(qemu_ram_get_host_addr(rb), rb->mmap_length,
+ QEMU_MADV_SPLIT)) {
+ error_report("%s: madvise(MADV_SPLIT) required for doublemap",
+ __func__);
+ return -1;
+ }
+
/*
* Firstly, we remap the same ramblock into another range of
* virtual address, so that we can write to the pages without
@@ -3898,6 +3911,11 @@ static int migrate_hugetlb_doublemap_init(void)
*/
addr = ramblock_file_map(rb);
if (addr == MAP_FAILED) {
+ /*
+ * No need to undo MADV_SPLIT because this is dest node and
+ * we're going to bail out anyway. Leave that for mm exit
+ * to clean things up.
+ */
ret = -errno;
error_report("%s: Duplicate mapping for hugetlb ramblock '%s'"
"failed: %s", __func__, qemu_ram_get_idstr(rb),
--
2.37.3
