multifd: Create property multifd-flush-after-each-section

We used to flush all channels at the end of each RAM section
sent.  That is not needed, so preparing to only flush after a full
iteration through all the RAM.

Default value of the property is false.  But we return "true" in
migrate_multifd_flush_after_each_section() until we implement the code
in following patches.

Signed-off-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Acked-by: Peter Xu <peterx@redhat.com>

---

Rename each-iteration to after-each-section
Rename multifd-sync-after-each-section to
       multifd-flush-after-each-section
Move to machine-8.0 (peter)

1 files changed, 12 insertions, 0 deletions

diff --git a/migration/migration.h b/migration/migration.h
index 2b71df8..e2247d7 100644
--- a/migration/migration.h
+++ b/migration/migration.h
@@ -405,6 +405,18 @@ struct MigrationState {
     bool preempt_pre_7_2;
 
     /*
+     * flush every channel after each section sent.
+     *
+     * This assures that we can't mix pages from one iteration through
+     * ram pages with pages for the following iteration.  We really
+     * only need to do this flush after we have go through all the
+     * dirty pages.  For historical reasons, we do that after each
+     * section.  This is suboptimal (we flush too many times).
+     * Default value is false.  Setting this property has no effect
+     * until the patch that removes this comment.  (since 8.1)
+     */
+    bool multifd_flush_after_each_section;
+    /*
      * This decides the size of guest memory chunk that will be used
      * to track dirty bitmap clearing.  The size of memory chunk will
      * be GUEST_PAGE_SIZE << N.  Say, N=0 means we will clear dirty