From: Peter Xu <pet...@redhat.com> Add two documentations for mapped-ram migration on two spots that may not be extremely clear.
Reviewed-by: Fabiano Rosas <faro...@suse.de> Link: https://lore.kernel.org/r/20240301091524.39900-1-pet...@redhat.com Cc: Prasad Pandit <ppan...@redhat.com> [peterx: fix two English errors per Prasad] Signed-off-by: Peter Xu <pet...@redhat.com> --- migration/multifd.c | 12 ++++++++++++ migration/ram.c | 8 +++++++- 2 files changed, 19 insertions(+), 1 deletion(-) diff --git a/migration/multifd.c b/migration/multifd.c index b4e5a9dfcc..d4a44da559 100644 --- a/migration/multifd.c +++ b/migration/multifd.c @@ -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; diff --git a/migration/ram.c b/migration/ram.c index 1f1b5297cf..c79e3de521 100644 --- a/migration/ram.c +++ b/migration/ram.c @@ -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(); } -- 2.44.0
