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migration/multifd: Document two places for mapped-ram

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Add two documentations for mapped-ram migration on two spots that may not
be extremely clear.

Reviewed-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20240301091524.39900-1-peterx@redhat.com
Cc: Prasad Pandit <ppandit@redhat.com>
[peterx: fix two English errors per Prasad]
Signed-off-by: Peter Xu <peterx@redhat.com>
This commit is contained in:
Peter Xu 2024-03-01 17:15:24 +08:00
parent 7a09f09283
commit 1a6e217c35
2 changed files with 19 additions and 1 deletions
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12
migration/multifd.c
View file

@ -709,6 +709,18 @@ static bool multifd_send_cleanup_channel(MultiFDSendParams *p, Error **errp)
{
if (p->c) {
migration_ioc_unregister_yank(p->c);
/*
* An explicit close() on the channel here is normally not
* required, but can be helpful for "file:" iochannels, where it
* will include fdatasync() to make sure the data is flushed to the
* disk backend.
*
* The object_unref() cannot guarantee that because: (1) finalize()
* of the iochannel is only triggered on the last reference, and
* it's not guaranteed that we always hold the last refcount when
* reaching here, and, (2) even if finalize() is invoked, it only
* does a close(fd) without data flush.
*/
qio_channel_close(p->c, &error_abort);
object_unref(OBJECT(p->c));
p->c = NULL;

8
migration/ram.c
View file

@ -4258,7 +4258,13 @@ static int ram_load_precopy(QEMUFile *f)
switch (flags & ~RAM_SAVE_FLAG_CONTINUE) {
case RAM_SAVE_FLAG_MEM_SIZE:
ret = parse_ramblocks(f, addr);
/*
* For mapped-ram migration (to a file) using multifd, we sync
* once and for all here to make sure all tasks we queued to
* multifd threads are completed, so that all the ramblocks
* (including all the guest memory pages within) are fully
* loaded after this sync returns.
*/
if (migrate_mapped_ram()) {
multifd_recv_sync_main();
}