Re: [Qemu-devel] [RFC PATCH 07/17] COLO buffer: implement colo buffer as well as QEMUFileOps based on it

[Hongyang Yang]

Hi

在 08/01/2014 10:52 PM, Dr. David Alan Gilbert 写道:
> * Yang Hongyang (address@hidden) wrote:
> > We need a buffer to store migration data.
> >
> > On save side:
> >    all saved data was write into colo buffer first, so that we can know
> > the total size of the migration data. this can also separate the data
> > transmission from colo control data, we use colo control data over
> > socket fd to synchronous both side's stat.
> >
> > On restore side:
> >    all migration data was read into colo buffer first, then load data
> > from the buffer: If network error happens while data transmission,
> > the slaver can still functinal because the migration data are not yet
> > loaded.
>
> This is very similar to the QEMUSizedBuffer based QEMUFile's that Stefan Berger
> wrote and that I use in both my postcopy and BER patchsets:
>
>   http://lists.gnu.org/archive/html/qemu-devel/2014-07/msg00846.html
>
>   (and to the similar code from Isaku Yamahata).
>
> I think we should be able to use a shared version even if we need some changes.

I've being using this patch as COLO buffer, see my latest branch:
https://github.com/macrosheep/qemu/tree/colo_v0.4

But this QEMUSizedBuffer does not exactly match our needs, although it can work.
We need a static buffer that lives through COLO process so that we don't need
to alloc/free buffers every checkpoint. Currently open the buffer for write
always alloc a new buffer, I think I need the following modification:

1. ability to open an existing QEMUSizedBuffer for write
2. a reset_buf() api, that will clear buffered data, or just rewind QEMUFile
   related to the buffer is enough.

> > Signed-off-by: Yang Hongyang <address@hidden>
> > ---
> >   migration-colo.c | 112 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >   1 file changed, 112 insertions(+)
> >
> > diff --git a/migration-colo.c b/migration-colo.c
> > index d566b9d..b90d9b6 100644
> > --- a/migration-colo.c
> > +++ b/migration-colo.c
> > @@ -11,6 +11,7 @@
> >   #include "qemu/main-loop.h"
> >   #include "qemu/thread.h"
> >   #include "block/coroutine.h"
> > +#include "qemu/error-report.h"
> >   #include "migration/migration-colo.h"
> >
> >   static QEMUBH *colo_bh;
> > @@ -20,14 +21,122 @@ bool colo_supported(void)
> >       return true;
> >   }
> >
> > +/* colo buffer */
> > +
> > +#define COLO_BUFFER_BASE_SIZE (1000*1000*4ULL)
> > +#define COLO_BUFFER_MAX_SIZE (1000*1000*1000*10ULL)
>
> Powers of 2 are nicer!
>
> Dave
> --
> Dr. David Alan Gilbert / address@hidden / Manchester, UK
> .

--
Thanks,
Yang.