When the zero page detection is done in the multifd threads, we need
to iterate the second part of the pages->offset array and clear the
file bitmap for each zero page. The piece of code we merged to do that
is wrong.
The reason this has passed all the tests is because the bitmap is
initialized with zeroes already, so clearing the bits only really has
an effect during live migration and when a data page goes from having
data to no data.
Fixes: 303e6f54f9 ("migration/multifd: Implement zero page transmission on the multifd thread.")
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20240321201242.6009-1-farosas@suse.de
Signed-off-by: Peter Xu <peterx@redhat.com>
This reverts commit decdc76772 in full
and also the relevant migration-tests from
7a09f09283.
After the addition of the new QAPI-based migration address API in 8.2
we've been converting an "fd:" URI into a SocketAddress, missing the
fact that the "fd:" syntax could also be used for a plain file instead
of a socket. This is a problem because the SocketAddress is part of
the API, so we're effectively asking users to create a "socket"
channel to pass in a plain file.
The easiest way to fix this situation is to deprecate the usage of
both SocketAddress and "fd:" when used with a plain file for
migration. Since this has been possible since 8.2, we can wait until
9.1 to deprecate it.
For 9.0, however, we should avoid adding further support to migration
to a plain file using the old "fd:" syntax or the new SocketAddress
API, and instead require the usage of either the old-style "file:" URI
or the FileMigrationArgs::filename field of the new API with the
"/dev/fdset/NN" syntax, both of which are already supported.
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20240319210941.1907-1-farosas@suse.de
Signed-off-by: Peter Xu <peterx@redhat.com>
1. Add zero_pages field in MultiFDPacket_t.
2. Implements the zero page detection and handling on the multifd
threads for non-compression, zlib and zstd compression backends.
3. Added a new value 'multifd' in ZeroPageDetection enumeration.
4. Adds zero page counters and updates multifd send/receive tracing
format to track the newly added counters.
Signed-off-by: Hao Xiang <hao.xiang@bytedance.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20240311180015.3359271-5-hao.xiang@linux.dev
Signed-off-by: Peter Xu <peterx@redhat.com>
We currently only need to clear the mapped-ram file bitmap from the
migration thread during save_zero_page.
We're about to add support for zero page detection on the multifd
thread, so allow ramblock_set_file_bmap_atomic() to also clear the
bits.
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20240311180015.3359271-3-hao.xiang@linux.dev
Signed-off-by: Peter Xu <peterx@redhat.com>
If we receive a file descriptor that points to a regular file, there's
nothing stopping us from doing multifd migration with mapped-ram to
that file.
Enable the fd: URI to work with multifd + mapped-ram.
Note that the fds passed into multifd are duplicated because we want
to avoid cross-thread effects when doing cleanup (i.e. close(fd)). The
original fd doesn't need to be duplicated because monitor_get_fd()
transfers ownership to the caller.
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Peter Xu <peterx@redhat.com>
Link: https://lore.kernel.org/r/20240229153017.2221-23-farosas@suse.de
Signed-off-by: Peter Xu <peterx@redhat.com>
For the incoming mapped-ram migration we need to read the ramblock
headers, get the pages bitmap and send the host address of each
non-zero page to the multifd channel thread for writing.
Usage on HMP is:
(qemu) migrate_set_capability multifd on
(qemu) migrate_set_capability mapped-ram on
(qemu) migrate_incoming file:migfile
(the ram.h include needs to move because we've been previously relying
on it being included from migration.c. Now file.h will start including
multifd.h before migration.o is processed)
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20240229153017.2221-22-farosas@suse.de
Signed-off-by: Peter Xu <peterx@redhat.com>
The new mapped-ram stream format uses a file transport and puts ram
pages in the migration file at their respective offsets and can be
done in parallel by using the pwritev system call which takes iovecs
and an offset.
Add support to enabling the new format along with multifd to make use
of the threading and page handling already in place.
This requires multifd to stop sending headers and leaving the stream
format to the mapped-ram code. When it comes time to write the data, we
need to call a version of qio_channel_write that can take an offset.
Usage on HMP is:
(qemu) stop
(qemu) migrate_set_capability multifd on
(qemu) migrate_set_capability mapped-ram on
(qemu) migrate_set_parameter max-bandwidth 0
(qemu) migrate_set_parameter multifd-channels 8
(qemu) migrate file:migfile
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20240229153017.2221-21-farosas@suse.de
Signed-off-by: Peter Xu <peterx@redhat.com>
Allow multifd to open file-backed channels. This will be used when
enabling the mapped-ram migration stream format which expects a
seekable transport.
The QIOChannel read and write methods will use the preadv/pwritev
versions which don't update the file offset at each call so we can
reuse the fd without re-opening for every channel.
Contrary to the socket migration, the file migration doesn't need an
asynchronous channel creation process, so expose
multifd_channel_connect() and call it directly.
Note that this is just setup code and multifd cannot yet make use of
the file channels.
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Peter Xu <peterx@redhat.com>
Link: https://lore.kernel.org/r/20240229153017.2221-18-farosas@suse.de
Signed-off-by: Peter Xu <peterx@redhat.com>
Currently multifd does not need to have knowledge of pages on the
receiving side because all the information needed is within the
packets that come in the stream.
We're about to add support to mapped-ram migration, which cannot use
packets because it expects the ramblock section in the migration file
to contain only the guest pages data.
Add a data structure to transfer pages between the ram migration code
and the multifd receiving threads.
We don't want to reuse MultiFDPages_t for two reasons:
a) multifd threads don't really need to know about the data they're
receiving.
b) the receiving side has to be stopped to load the pages, which means
we can experiment with larger granularities than page size when
transferring data.
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20240229153017.2221-16-farosas@suse.de
Signed-off-by: Peter Xu <peterx@redhat.com>
For the upcoming support to the new 'mapped-ram' migration stream
format, we cannot use multifd packets because each write into the
ramblock section in the migration file is expected to contain only the
guest pages. They are written at their respective offsets relative to
the ramblock section header.
There is no space for the packet information and the expected gains
from the new approach come partly from being able to write the pages
sequentially without extraneous data in between.
The new format also simply doesn't need the packets and all necessary
information can be taken from the standard migration headers with some
(future) changes to multifd code.
Use the presence of the mapped-ram capability to decide whether to
send packets.
This only moves code under multifd_use_packets(), it has no effect for
now as mapped-ram cannot yet be enabled with multifd.
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20240229153017.2221-15-farosas@suse.de
Signed-off-by: Peter Xu <peterx@redhat.com>
Some minor cleanups and documentation for multifd_recv_sync_main.
Use thread_count as done in other parts of the code. Remove p->id from
the multifd_recv_state sync, since that is global and not tied to a
channel. Add documentation for the sync steps.
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20240229153017.2221-2-farosas@suse.de
Signed-off-by: Peter Xu <peterx@redhat.com>
Both socket_send_channel_destroy() and multifd_send_channel_destroy() are
unnecessary wrappers to destroy an IOC, as the only thing to do is to
release the final IOC reference. We have plenty of code that destroys an
IOC using direct unref() already; keep that style.
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20240222095301.171137-6-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
outgoing_args is a global cache of socket address to be reused in multifd.
Freeing the cache in per-channel destructor is more or less a hack. Move
it to multifd_send_cleanup_state() so it only get checked once. Use a
small helper to do so because it's internal of socket.c.
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20240222095301.171137-5-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
With a clear definition of p->c protocol, where we only set it up if the
channel is fully established (TLS or non-TLS), registered_yank boolean will
have equal meaning of "p->c != NULL".
Drop registered_yank by checking p->c instead.
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20240222095301.171137-3-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
Commit a1af605bd5 ("migration/multifd: fix hangup with TLS-Multifd due to
blocking handshake") introduced a thread for TLS channels, which will
resolve the issue on blocking the main thread. However in the same commit
p->c is slightly abused just to be able to pass over the pointer "p" into
the thread.
That's the major reason we'll need to conditionally free the io channel in
the fault paths.
To clean it up, using a separate structure to pass over both "p" and "tioc"
in the tls handshake thread. Then we can make it a rule that p->c will
never be set until the channel is completely setup. With that, we can drop
the tricky conditional unref of the io channel in the error path.
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20240222095301.171137-2-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
It is possible that one of the multifd channels fails to be created at
multifd_new_send_channel_async() while the rest of the channel
creation tasks are still in flight.
This could lead to multifd_save_cleanup() executing the
qemu_thread_join() loop too early and not waiting for the threads
which haven't been created yet, leading to the freeing of resources
that the newly created threads will try to access and crash.
Add a synchronization point after which there will be no attempts at
thread creation and therefore calling multifd_save_cleanup() past that
point will ensure it properly waits for the threads.
A note about performance: Prior to this patch, if a channel took too
long to be established, other channels could finish connecting first
and already start taking load. Now we're bounded by the
slowest-connecting channel.
Reported-by: Avihai Horon <avihaih@nvidia.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20240206215118.6171-7-farosas@suse.de
Signed-off-by: Peter Xu <peterx@redhat.com>
During multifd channel creation (multifd_send_new_channel_async) when
TLS is enabled, the multifd_channel_connect function is called twice,
once to create the TLS handshake thread and another time after the
asynchrounous TLS handshake has finished.
This creates a slightly confusing call stack where
multifd_channel_connect() is called more times than the number of
channels. It also splits error handling between the two callers of
multifd_channel_connect() causing some code duplication. Lastly, it
gets in the way of having a single point to determine whether all
channel creation tasks have been initiated.
Refactor the code to move the reentrancy one level up at the
multifd_new_send_channel_async() level, de-duplicating the error
handling and allowing for the next patch to introduce a
synchronization point common to all the multifd channel creation,
regardless of TLS.
Note that the previous code would never fail once p->c had been set.
This patch changes this assumption, which affects refcounting, so add
comments around object_unref to explain the situation.
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20240206215118.6171-6-farosas@suse.de
Signed-off-by: Peter Xu <peterx@redhat.com>
Fabiano RosasandPeter Xu
Hao XiangandPeter Xu