* Andrey Gruzdev (andrey.gruz...@virtuozzo.com) wrote:
> On 19.01.2021 21:49, Dr. David Alan Gilbert wrote:
> > * Andrey Gruzdev (andrey.gruz...@virtuozzo.com) wrote:
> > > Introducing implementation of 'background' snapshot thread
> > > which in overall follows the logic of precopy migration
> > > while internally utilizes completely different mechanism
> > > to 'freeze' vmstate at the start of snapshot creation.
> > >
> > > This mechanism is based on userfault_fd with wr-protection
> > > support and is Linux-specific.
> > I noticed there weren't any bdrv_ calls in here; I guess with a snapshot
> > you still have the source running so still have it accessing the disk;
> > do you do anything to try and wire the ram snapshotting up to disk
> > snapshotting?
>
> Block-related manipulations should be done externally, I think.
> So create backing images for RW nodes, then stop VM, switch block graph
> and start background snapshot. Something like create 'virsh
> snapshot-create-as'
> does, but in other sequence.
If you get a chance it would be great if you could put together an
example of doing the combination RAM+block; that way we find out if there's
anything silly missing.
Dave
> //
>
> > > Signed-off-by: Andrey Gruzdev <andrey.gruz...@virtuozzo.com>
> > > Acked-by: Peter Xu <pet...@redhat.com>
> > > ---
> > > migration/migration.c | 255 +++++++++++++++++++++++++++++++++++++++++-
> > > migration/migration.h | 3 +
> > > migration/ram.c | 2 +
> > > migration/savevm.c | 1 -
> > > migration/savevm.h | 2 +
> > > 5 files changed, 260 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/migration/migration.c b/migration/migration.c
> > > index 2c2cb9ef01..0901a15ac5 100644
> > <snip>
> >
> > > - qemu_thread_create(&s->thread, "live_migration", migration_thread, s,
> > > - QEMU_THREAD_JOINABLE);
> > > +
> > > + if (migrate_background_snapshot()) {
> > > + qemu_thread_create(&s->thread, "background_snapshot",
> > Unfortunately that wont work - there's a 14 character limit on
> > the thread name length; I guess we just shorten that to bg_snapshot
>
> Yep, missed that pthread_set_name_np() has a length limit)
>
> > Other than that,
> >
> >
> >
> > Reviewed-by: Dr. David Alan Gilbert <dgilb...@redhat.com>
> >
> > > + bg_migration_thread, s, QEMU_THREAD_JOINABLE);
> > > + } else {
> > > + qemu_thread_create(&s->thread, "live_migration",
> > > + migration_thread, s, QEMU_THREAD_JOINABLE);
> > > + }
> > > s->migration_thread_running = true;
> > > }
> > > diff --git a/migration/migration.h b/migration/migration.h
> > > index f40338cfbf..0723955cd7 100644
> > > --- a/migration/migration.h
> > > +++ b/migration/migration.h
> > > @@ -20,6 +20,7 @@
> > > #include "qemu/thread.h"
> > > #include "qemu/coroutine_int.h"
> > > #include "io/channel.h"
> > > +#include "io/channel-buffer.h"
> > > #include "net/announce.h"
> > > #include "qom/object.h"
> > > @@ -147,8 +148,10 @@ struct MigrationState {
> > > /*< public >*/
> > > QemuThread thread;
> > > + QEMUBH *vm_start_bh;
> > > QEMUBH *cleanup_bh;
> > > QEMUFile *to_dst_file;
> > > + QIOChannelBuffer *bioc;
> > > /*
> > > * Protects to_dst_file pointer. We need to make sure we won't
> > > * yield or hang during the critical section, since this lock will
> > > diff --git a/migration/ram.c b/migration/ram.c
> > > index 5707382db1..05fe0c8592 100644
> > > --- a/migration/ram.c
> > > +++ b/migration/ram.c
> > > @@ -1471,6 +1471,7 @@ static RAMBlock *poll_fault_page(RAMState *rs,
> > > ram_addr_t *offset)
> > > page_address = (void *) uffd_msg.arg.pagefault.address;
> > > bs = qemu_ram_block_from_host(page_address, false, offset);
> > > assert(bs && (bs->flags & RAM_UF_WRITEPROTECT) != 0);
> > > +
> > > return bs;
> > > }
> > > #endif /* CONFIG_LINUX */
> > > @@ -1836,6 +1837,7 @@ static void ram_save_host_page_post(RAMState *rs,
> > > PageSearchStatus *pss,
> > > /* Un-protect memory range. */
> > > res = uffd_change_protection(rs->uffdio_fd, page_address,
> > > run_length,
> > > false, false);
> > > +
> > > /* We don't want to override existing error from
> > > ram_save_host_page(). */
> > > if (res < 0 && *res_override >= 0) {
> > > *res_override = res;
> > > diff --git a/migration/savevm.c b/migration/savevm.c
> > > index 27e842812e..dd4ad0aaaf 100644
> > > --- a/migration/savevm.c
> > > +++ b/migration/savevm.c
> > > @@ -1354,7 +1354,6 @@ int
> > > qemu_savevm_state_complete_precopy_iterable(QEMUFile *f, bool in_postcopy)
> > > return 0;
> > > }
> > > -static
> > > int qemu_savevm_state_complete_precopy_non_iterable(QEMUFile *f,
> > > bool in_postcopy,
> > > bool
> > > inactivate_disks)
> > > diff --git a/migration/savevm.h b/migration/savevm.h
> > > index ba64a7e271..aaee2528ed 100644
> > > --- a/migration/savevm.h
> > > +++ b/migration/savevm.h
> > > @@ -64,5 +64,7 @@ int qemu_loadvm_state(QEMUFile *f);
> > > void qemu_loadvm_state_cleanup(void);
> > > int qemu_loadvm_state_main(QEMUFile *f, MigrationIncomingState *mis);
> > > int qemu_load_device_state(QEMUFile *f);
> > > +int qemu_savevm_state_complete_precopy_non_iterable(QEMUFile *f,
> > > + bool in_postcopy, bool inactivate_disks);
> > > #endif
> > > --
> > > 2.25.1
> > >
>
> --
> Andrey Gruzdev, Principal Engineer
> Virtuozzo GmbH +7-903-247-6397
> virtuzzo.com
>
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
