This implements the zero page detection and handling on the multifd
threads.
Signed-off-by: Hao Xiang <hao.xiang@bytedance.com>
---
migration/multifd.c | 62 +++++++++++++++++++++++++++++++++++++++++----
migration/multifd.h | 5 ++++
2 files changed, 62 insertions(+), 5 deletions(-)
diff --git a/migration/multifd.c b/migration/multifd.c
index a20d0ed10e..c031f947c7 100644
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -11,6 +11,7 @@
*/
#include "qemu/osdep.h"
+#include "qemu/cutils.h"
#include "qemu/rcu.h"
#include "exec/target_page.h"
#include "sysemu/sysemu.h"
@@ -278,6 +279,12 @@ static void multifd_send_fill_packet(MultiFDSendParams *p)
packet->offset[i] = cpu_to_be64(temp);
}
+ for (i = 0; i < p->zero_num; i++) {
+ /* there are architectures where ram_addr_t is 32 bit */
+ uint64_t temp = p->zero[i];
+
+ packet->offset[p->normal_num + i] = cpu_to_be64(temp);
+ }
}
static int multifd_recv_unfill_packet(MultiFDRecvParams *p, Error **errp)
@@ -360,6 +367,18 @@ static int multifd_recv_unfill_packet(MultiFDRecvParams *p, Error **errp)
p->normal[i] = offset;
}
+ for (i = 0; i < p->zero_num; i++) {
+ uint64_t offset = be64_to_cpu(packet->offset[p->normal_num + i]);
+
+ if (offset > (p->block->used_length - p->page_size)) {
+ error_setg(errp, "multifd: offset too long %" PRIu64
+ " (max " RAM_ADDR_FMT ")",
+ offset, p->block->used_length);
+ return -1;
+ }
+ p->zero[i] = offset;
+ }
+
return 0;
}
@@ -658,13 +677,37 @@ int multifd_send_sync_main(void)
return 0;
}
+static void zero_page_check_send(MultiFDSendParams *p)
+{
+ /*
+ * QEMU older than 9.0 don't understand zero page
+ * on multifd channel. This switch is required to
+ * maintain backward compatibility.
+ */
+ bool use_multifd_zero_page = migrate_multifd_zero_page();
+ RAMBlock *rb = p->pages->block;
+
+ for (int i = 0; i < p->pages->num; i++) {
+ uint64_t offset = p->pages->offset[i];
+ if (use_multifd_zero_page &&
+ buffer_is_zero(rb->host + offset, p->page_size)) {
+ p->zero[p->zero_num] = offset;
+ p->zero_num++;
+ ram_release_page(rb->idstr, offset);
+ } else {
+ p->normal[p->normal_num] = offset;
+ p->normal_num++;
+ }
+ }
+}
+
static void *multifd_send_thread(void *opaque)
{
MultiFDSendParams *p = opaque;
MigrationThread *thread = NULL;
Error *local_err = NULL;
- int ret = 0;
bool use_zero_copy_send = migrate_zero_copy_send();
+ int ret = 0;
thread = migration_threads_add(p->name, qemu_get_thread_id());
@@ -699,10 +742,7 @@ static void *multifd_send_thread(void *opaque)
p->iovs_num = 1;
}
- for (int i = 0; i < p->pages->num; i++) {
- p->normal[p->normal_num] = p->pages->offset[i];
- p->normal_num++;
- }
+ zero_page_check_send(p);
if (p->normal_num) {
ret = multifd_send_state->ops->send_prepare(p, &local_err);
@@ -1107,6 +1147,16 @@ void multifd_recv_sync_main(void)
trace_multifd_recv_sync_main(multifd_recv_state->packet_num);
}
+static void zero_page_check_recv(MultiFDRecvParams *p)
+{
+ for (int i = 0; i < p->zero_num; i++) {
+ void *page = p->host + p->zero[i];
+ if (!buffer_is_zero(page, p->page_size)) {
+ memset(page, 0, p->page_size);
+ }
+ }
+}
+
static void *multifd_recv_thread(void *opaque)
{
MultiFDRecvParams *p = opaque;
@@ -1153,6 +1203,8 @@ static void *multifd_recv_thread(void *opaque)
}
}
+ zero_page_check_recv(p);
+
if (flags & MULTIFD_FLAG_SYNC) {
qemu_sem_post(&multifd_recv_state->sem_sync);
qemu_sem_wait(&p->sem_sync);
diff --git a/migration/multifd.h b/migration/multifd.h
index 6be9b2f6c1..7448cb1aa9 100644
--- a/migration/multifd.h
+++ b/migration/multifd.h
@@ -53,6 +53,11 @@ typedef struct {
uint32_t unused32[1]; /* Reserved for future use */
uint64_t unused64[3]; /* Reserved for future use */
char ramblock[256];
+ /*
+ * This array contains the pointers to:
+ * - normal pages (initial normal_pages entries)
+ * - zero pages (following zero_pages entries)
+ */
uint64_t offset[];
} __attribute__((packed)) MultiFDPacket_t;
--
2.30.2