migration/multifd: Implement zero page transmission on the multifd thread.

1. Add zero_pages field in MultiFDPacket_t.
2. Implements the zero page detection and handling on the multifd
threads for non-compression, zlib and zstd compression backends.
3. Added a new value 'multifd' in ZeroPageDetection enumeration.
4. Adds zero page counters and updates multifd send/receive tracing
format to track the newly added counters.

Signed-off-by: Hao Xiang <hao.xiang@bytedance.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20240311180015.3359271-5-hao.xiang@linux.dev
Signed-off-by: Peter Xu <peterx@redhat.com>

1 files changed, 15 insertions, 5 deletions

diff --git a/migration/multifd-zstd.c b/migration/multifd-zstd.c
index cac236833d..02112255ad 100644
--- a/migration/multifd-zstd.c
+++ b/migration/multifd-zstd.c
@@ -118,16 +118,18 @@ static int zstd_send_prepare(MultiFDSendParams *p, Error **errp)
     int ret;
     uint32_t i;
 
-    multifd_send_prepare_header(p);
+    if (!multifd_send_prepare_common(p)) {
+        goto out;
+    }
 
     z->out.dst = z->zbuff;
     z->out.size = z->zbuff_len;
     z->out.pos = 0;
 
-    for (i = 0; i < pages->num; i++) {
+    for (i = 0; i < pages->normal_num; i++) {
         ZSTD_EndDirective flush = ZSTD_e_continue;
 
-        if (i == pages->num - 1) {
+        if (i == pages->normal_num - 1) {
             flush = ZSTD_e_flush;
         }
         z->in.src = p->pages->block->host + pages->offset[i];
@@ -161,10 +163,10 @@ static int zstd_send_prepare(MultiFDSendParams *p, Error **errp)
     p->iov[p->iovs_num].iov_len = z->out.pos;
     p->iovs_num++;
     p->next_packet_size = z->out.pos;
-    p->flags |= MULTIFD_FLAG_ZSTD;
 
+out:
+    p->flags |= MULTIFD_FLAG_ZSTD;
     multifd_send_fill_packet(p);
-
     return 0;
 }
 
@@ -257,6 +259,14 @@ static int zstd_recv(MultiFDRecvParams *p, Error **errp)
                    p->id, flags, MULTIFD_FLAG_ZSTD);
         return -1;
     }
+
+    multifd_recv_zero_page_process(p);
+
+    if (!p->normal_num) {
+        assert(in_size == 0);
+        return 0;
+    }
+
     ret = qio_channel_read_all(p->c, (void *)z->zbuff, in_size, errp);
 
     if (ret != 0) {