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Re: [PATCH v1 1/3] migration: Fix missing qemu_fflush() on buffer file i
From: |
Peter Xu |
Subject: |
Re: [PATCH v1 1/3] migration: Fix missing qemu_fflush() on buffer file in bg_migration_thread |
Date: |
Tue, 23 Mar 2021 10:54:57 -0400 |
On Tue, Mar 23, 2021 at 10:51:57AM +0300, Andrey Gruzdev wrote:
> On 22.03.2021 23:17, Peter Xu wrote:
> > On Fri, Mar 19, 2021 at 05:52:47PM +0300, Andrey Gruzdev wrote:
> > > Added missing qemu_fflush() on buffer file holding precopy device state.
> > > Increased initial QIOChannelBuffer allocation to 512KB to avoid reallocs.
> > > Typical configurations often require >200KB for device state and VMDESC.
> > >
> > > Signed-off-by: Andrey Gruzdev <andrey.gruzdev@virtuozzo.com>
> > > ---
> > > migration/migration.c | 4 +++-
> > > 1 file changed, 3 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/migration/migration.c b/migration/migration.c
> > > index ca8b97baa5..32b48fe9f5 100644
> > > --- a/migration/migration.c
> > > +++ b/migration/migration.c
> > > @@ -3812,7 +3812,7 @@ static void *bg_migration_thread(void *opaque)
> > > * with vCPUs running and, finally, write stashed non-RAM part of
> > > * the vmstate from the buffer to the migration stream.
> > > */
> > > - s->bioc = qio_channel_buffer_new(128 * 1024);
> > > + s->bioc = qio_channel_buffer_new(512 * 1024);
> > > qio_channel_set_name(QIO_CHANNEL(s->bioc), "vmstate-buffer");
> > > fb = qemu_fopen_channel_output(QIO_CHANNEL(s->bioc));
> > > object_unref(OBJECT(s->bioc));
> > > @@ -3866,6 +3866,8 @@ static void *bg_migration_thread(void *opaque)
> > > if (qemu_savevm_state_complete_precopy_non_iterable(fb, false,
> > > false)) {
> > > goto fail;
> > > }
> > > + qemu_fflush(fb);
> > What will happen if the vmstates are bigger than 512KB? Would the extra
> > data
> > be dropped?
>
> No, the buffer shall be reallocated and the original content shall be kept.
Oh right..
Would you comment above qemu_fflush() about it (maybe also move it right before
the call to qemu_put_buffer)? Otherwise it indeed looks more like an
optimization rather than a bugfix.
For the long term I think we'd better have a helper:
qemu_put_qio_channel_buffer(QEMUFile *file, QIOChannelBuffer *bioc)
So as to hide this flush operation, which is tricky. We'll have two users so
far:
bg_migration_completion
colo_do_checkpoint_transaction
IMHO it'll be nicer if you'd do it in this patch altogether!
Thanks,
--
Peter Xu
- [PATCH v1 0/3] migration: Fixes to the 'background-snapshot' code, Andrey Gruzdev, 2021/03/19
- [PATCH v1 1/3] migration: Fix missing qemu_fflush() on buffer file in bg_migration_thread, Andrey Gruzdev, 2021/03/19
- Re: [PATCH v1 1/3] migration: Fix missing qemu_fflush() on buffer file in bg_migration_thread, Peter Xu, 2021/03/22
- Re: [PATCH v1 1/3] migration: Fix missing qemu_fflush() on buffer file in bg_migration_thread, Andrey Gruzdev, 2021/03/23
- Re: [PATCH v1 1/3] migration: Fix missing qemu_fflush() on buffer file in bg_migration_thread,
Peter Xu <=
- Re: [PATCH v1 1/3] migration: Fix missing qemu_fflush() on buffer file in bg_migration_thread, Andrey Gruzdev, 2021/03/23
- Re: [PATCH v1 1/3] migration: Fix missing qemu_fflush() on buffer file in bg_migration_thread, Peter Xu, 2021/03/23
- Re: [PATCH v1 1/3] migration: Fix missing qemu_fflush() on buffer file in bg_migration_thread, Andrey Gruzdev, 2021/03/24
- Re: [PATCH v1 1/3] migration: Fix missing qemu_fflush() on buffer file in bg_migration_thread, Dr. David Alan Gilbert, 2021/03/24
- Re: [PATCH v1 1/3] migration: Fix missing qemu_fflush() on buffer file in bg_migration_thread, Peter Xu, 2021/03/24
[PATCH v1 3/3] migration: Pre-fault memory before starting background snasphot, Andrey Gruzdev, 2021/03/19
[PATCH v1 2/3] migration: Inhibit virtio-balloon for the duration of background snapshot, Andrey Gruzdev, 2021/03/19
Re: [PATCH v1 0/3] migration: Fixes to the 'background-snapshot' code, Peter Xu, 2021/03/23