From: Peter Xu <peterx@redhat.com>

Now we reset MultiFDPages_t object in the multifd sender thread in the
middle of the sending job.  That's not necessary, because the "*pages"
struct will not be reused anyway until pending_job is cleared.

Move that to the end after the job is completed, provide a helper to reset
a "*pages" object.  Use that same helper when free the object too.

This prepares us to keep using p->pages in the follow up patches, where we
may drop p->normal[].

Reviewed-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20240202102857.110210-5-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
---
 migration/multifd.c | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/migration/multifd.c b/migration/multifd.c
index 2c98023d67..5633ac245a 100644
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -172,6 +172,17 @@ void multifd_register_ops(int method, MultiFDMethods *ops)
     multifd_ops[method] = ops;
 }
 
+/* Reset a MultiFDPages_t* object for the next use */
+static void multifd_pages_reset(MultiFDPages_t *pages)
+{
+    /*
+     * We don't need to touch offset[] array, because it will be
+     * overwritten later when reused.
+     */
+    pages->num = 0;
+    pages->block = NULL;
+}
+
 static int multifd_send_initial_packet(MultiFDSendParams *p, Error **errp)
 {
     MultiFDInit_t msg = {};
@@ -248,9 +259,8 @@ static MultiFDPages_t *multifd_pages_init(uint32_t n)
 
 static void multifd_pages_clear(MultiFDPages_t *pages)
 {
-    pages->num = 0;
+    multifd_pages_reset(pages);
     pages->allocated = 0;
-    pages->block = NULL;
     g_free(pages->offset);
     pages->offset = NULL;
     g_free(pages);
@@ -704,8 +714,6 @@ static void *multifd_send_thread(void *opaque)
             p->flags = 0;
             p->num_packets++;
             p->total_normal_pages += p->normal_num;
-            p->pages->num = 0;
-            p->pages->block = NULL;
             qemu_mutex_unlock(&p->mutex);
 
             trace_multifd_send(p->id, packet_num, p->normal_num, flags,
@@ -732,6 +740,8 @@ static void *multifd_send_thread(void *opaque)
 
             stat64_add(&mig_stats.multifd_bytes,
                        p->next_packet_size + p->packet_len);
+
+            multifd_pages_reset(p->pages);
             p->next_packet_size = 0;
             qemu_mutex_lock(&p->mutex);
             p->pending_job--;
-- 
2.43.0