From: Peter Xu <peterx@redhat.com>
To: Andrey Gruzdev <andrey.gruzdev@virtuozzo.com>
Cc: Juan Quintela <quintela@redhat.com>,
Markus Armbruster <armbru@redhat.com>,
David Hildenbrand <david@redhat.com>,
qemu-devel@nongnu.org,
"Dr . David Alan Gilbert" <dgilbert@redhat.com>,
Paolo Bonzini <pbonzini@redhat.com>, Den Lunev <den@openvz.org>
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 [thread overview]
Message-ID: <20210323145457.GC6486@xz-x1> (raw)
In-Reply-To: <2fb49f83-e31c-8c93-50b7-833026b06518@virtuozzo.com>
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
next prev parent reply other threads:[~2021-03-23 14:57 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-19 14:52 [PATCH v1 0/3] migration: Fixes to the 'background-snapshot' code Andrey Gruzdev
2021-03-19 14:52 ` [PATCH v1 1/3] migration: Fix missing qemu_fflush() on buffer file in bg_migration_thread Andrey Gruzdev
2021-03-22 20:17 ` Peter Xu
2021-03-23 7:51 ` Andrey Gruzdev
2021-03-23 14:54 ` Peter Xu [this message]
2021-03-23 17:21 ` Andrey Gruzdev
2021-03-23 18:35 ` Peter Xu
2021-03-24 7:48 ` Andrey Gruzdev
2021-03-24 17:35 ` Dr. David Alan Gilbert
2021-03-24 18:50 ` Peter Xu
2021-03-19 14:52 ` [PATCH v1 2/3] migration: Inhibit virtio-balloon for the duration of background snapshot Andrey Gruzdev
2021-03-19 14:52 ` [PATCH v1 3/3] migration: Pre-fault memory before starting background snasphot Andrey Gruzdev
2021-03-23 22:21 ` [PATCH v1 0/3] migration: Fixes to the 'background-snapshot' code Peter Xu
2021-03-24 8:09 ` Andrey Gruzdev
2021-03-24 15:41 ` Peter Xu
2021-03-25 9:51 ` Andrey Gruzdev
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