migration/postcopy: not necessary to do discard when canonicalizing bitmap

All pages, either partially sent or partially dirty, will be discarded in
postcopy_send_discard_bm_ram(), since we update the unsentmap to be
unsentmap = unsentmap | dirty in ram_postcopy_send_discard_bitmap().

This is not necessary to do discard when canonicalizing bitmap. And by
doing so, we separate the page discard into two individual steps:

  * canonicalize bitmap
  * discard page

Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
Message-Id: <20190819061843.28642-2-richardw.yang@linux.intel.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

diff --git a/migration/ram.c b/migration/ram.c
index 01df3267676514e6551d157b4ccc545fdd1f9c1a..57d1a4627ee292bfa1b628fcdc9bc827f5a20bd7 100644 (file)
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -2928,7 +2928,7 @@ static int postcopy_each_ram_send_discard(MigrationState *ms)
 }
 
 /**
- * postcopy_chunk_hostpages_pass: canocalize bitmap in hostpages
+ * postcopy_chunk_hostpages_pass: canonicalize bitmap in hostpages
  *
  * Helper for postcopy_chunk_hostpages; it's called twice to
  * canonicalize the two bitmaps, that are similar, but one is
@@ -2991,18 +2991,6 @@ static void postcopy_chunk_hostpages_pass(MigrationState *ms, bool unsent_pass,
                                                              host_ratio);
             run_start = QEMU_ALIGN_UP(run_start, host_ratio);
 
-            /* Tell the destination to discard this page */
-            if (unsent_pass || !test_bit(fixup_start_addr, unsentmap)) {
-                /* For the unsent_pass we:
-                 *     discard partially sent pages
-                 * For the !unsent_pass (dirty) we:
-                 *     discard partially dirty pages that were sent
-                 *     (any partially sent pages were already discarded
-                 *     by the previous unsent_pass)
-                 */
-                postcopy_discard_send_range(ms, fixup_start_addr, host_ratio);
-            }
-
             /* Clean up the bitmap */
             for (page = fixup_start_addr;
                  page < fixup_start_addr + host_ratio; page++) {