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Re: [PATCH v3 03/17] migration: Block migration comment or code is wrong

From: Avihai Horon
Subject: Re: [PATCH v3 03/17] migration: Block migration comment or code is wrong
Date: Thu, 10 Nov 2022 15:38:44 +0200
User-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.4.1

On 08/11/2022 20:36, Vladimir Sementsov-Ogievskiy wrote:
External email: Use caution opening links or attachments

On 11/3/22 19:16, Avihai Horon wrote:
From: Juan Quintela <quintela@redhat.com>

And it appears that what is wrong is the code. During bulk stage we
need to make sure that some block is dirty, but no games with
max_size at all.

:) That made me interested in, why we need this one block, so I decided to search through the history.

And what I see? Haha, that was my commit 04636dc410b163c "migration/block: fix pending() return value" [1], which you actually revert with this patch.

So, at least we should note, that it's a revert of [1].

Still that this will reintroduce the bug fixed by [1].

As I understand the problem is (was) that in block_save_complete() we finalize only dirty blocks, but don't finalize the bulk phase if it's not finalized yet. So, we can fix block_save_complete() to finalize the bulk phase, instead of hacking with pending in [1].

Interesting, why we need this one block, described in the comment you refer to? Was it an incomplete workaround for the same problem, described in [1]? If so, we can fix block_save_complete() and remove this if() together with the comment from block_save_pending().

I am not familiar with block migration.
I can drop this patch in next version.

Juan/Stefan, could you help here?

Signed-off-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
  migration/block.c | 4 ++--
  1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/migration/block.c b/migration/block.c
index b3d680af75..39ce4003c6 100644
--- a/migration/block.c
+++ b/migration/block.c
@@ -879,8 +879,8 @@ static void block_save_pending(void *opaque, uint64_t max_size,

      /* Report at least one block pending during bulk phase */
-    if (pending <= max_size && !block_mig_state.bulk_completed) {
-        pending = max_size + BLK_MIG_BLOCK_SIZE;
+    if (!pending && !block_mig_state.bulk_completed) {
+        pending = BLK_MIG_BLOCK_SIZE;


Best regards,

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