[Qemu-devel] [PULL 07/14] mirror: efficiently zero out target

[Jeff Cody <jcody@redhat.com>]

From: "Denis V. Lunev" <den@openvz.org>

With a bdrv_co_write_zeroes method on a target BDS and when this method
is working as indicated by the bdrv_can_write_zeroes_with_unmap(), zeroes
will not be placed into the wire. Thus the target could be very efficiently
zeroed out. This should be done with the largest chunk possible.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Reviewed-by: Vladimir Sementsov-Ogievskiy<vsementsov@virtuozzo.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Message-id: 1468503209-19498-8-git-send-email-den@openvz.org
CC: Stefan Hajnoczi <stefanha@redhat.com>
CC: Kevin Wolf <kwolf@redhat.com>
CC: Max Reitz <mreitz@redhat.com>
CC: Jeff Cody <jcody@redhat.com>
CC: Eric Blake <eblake@redhat.com>
Signed-off-by: Jeff Cody <jcody@redhat.com>
---
 block/mirror.c | 28 ++++++++++++++++++++++++++--
 1 file changed, 26 insertions(+), 2 deletions(-)

diff --git a/block/mirror.c b/block/mirror.c
index b7b1ded..0262b03 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -538,8 +538,32 @@ static int coroutine_fn mirror_dirty_init(MirrorBlockJob *s)
     end = s->bdev_length / BDRV_SECTOR_SIZE;
 
     if (base == NULL && !bdrv_has_zero_init(target_bs)) {
-        bdrv_set_dirty_bitmap(s->dirty_bitmap, 0, end);
-        return 0;
+        if (!bdrv_can_write_zeroes_with_unmap(target_bs)) {
+            bdrv_set_dirty_bitmap(s->dirty_bitmap, 0, end);
+            return 0;
+        }
+
+        for (sector_num = 0; sector_num < end; ) {
+            int nb_sectors = MIN(end - sector_num,
+                QEMU_ALIGN_DOWN(INT_MAX, s->granularity) >> BDRV_SECTOR_BITS);
+
+            mirror_throttle(s);
+
+            if (block_job_is_cancelled(&s->common)) {
+                return 0;
+            }
+
+            if (s->in_flight >= MAX_IN_FLIGHT) {
+                trace_mirror_yield(s, s->in_flight, s->buf_free_count, -1);
+                mirror_wait_for_io(s);
+                continue;
+            }
+
+            mirror_do_zero_or_discard(s, sector_num, nb_sectors, false);
+            sector_num += nb_sectors;
+        }
+
+        mirror_drain(s);
     }
 
     /* First part, loop on the sectors and initialize the dirty bitmap.  */
-- 
1.9.3