From: Prasad Pandit <p...@fedoraproject.org>
During multifd migration, zero pages are are written if
they are migrated more than ones.
This may result in a migration hang issue when Multifd
and Postcopy are enabled together.
When Postcopy is enabled, always write zero pages as and
when they are migrated.
Signed-off-by: Prasad Pandit <p...@fedoraproject.org>
---
migration/multifd-zero-page.c | 22 ++++++++++++++++++++--
1 file changed, 20 insertions(+), 2 deletions(-)
v10: new patch, not present in v9 or earlier versions.
diff --git a/migration/multifd-zero-page.c b/migration/multifd-zero-page.c
index dbc1184921..9bfb3ef803 100644
--- a/migration/multifd-zero-page.c
+++ b/migration/multifd-zero-page.c
@@ -85,9 +85,27 @@ void multifd_recv_zero_page_process(MultiFDRecvParams *p)
{
for (int i = 0; i < p->zero_num; i++) {
void *page = p->host + p->zero[i];
- if (ramblock_recv_bitmap_test_byte_offset(p->block, p->zero[i])) {
+
+ /*
+ * During multifd migration zero page is written to the memory
+ * only if it is migrated more than ones.
+ *
+ * It becomes a problem when both Multifd & Postcopy options are
+ * enabled. If the zero page which was skipped during multifd phase,
+ * is accessed during the Postcopy phase of the migration, a page
+ * fault occurs. But this page fault is not served because the
+ * 'receivedmap' says the zero page is already received. Thus the
+ * migration hangs.
+ *
+ * When Postcopy is enabled, always write the zero page as and when
+ * it is migrated.
+ *
+ */
+ if (migrate_postcopy_ram() ||
+ ramblock_recv_bitmap_test_byte_offset(p->block, p->zero[i])) {
memset(page, 0, multifd_ram_page_size());
- } else {
+ }
+ if (!ramblock_recv_bitmap_test_byte_offset(p->block, p->zero[i])) {
ramblock_recv_bitmap_set_offset(p->block, p->zero[i]);
}
}
--
2.49.0
