Re: [Xen-devel] [PATCH Remus v5 2/2] libxc/restore: implement Remus checkpointed restore

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Fri, 2015-05-15 at 09:32 +0800, Yang Hongyang wrote:
> 
> On 05/14/2015 09:05 PM, Ian Campbell wrote:
> > On Thu, 2015-05-14 at 18:06 +0800, Yang Hongyang wrote:
> >> With Remus, the restore flow should be:
> >> the first full migration stream -> { periodically restore stream }
> >>
> >> Signed-off-by: Yang Hongyang <yanghy@xxxxxxxxxxxxxx>
> >> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> >> CC: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
> >> CC: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
> >> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
> >> ---
> >>   tools/libxc/xc_sr_common.h  |  14 ++++++
> >>   tools/libxc/xc_sr_restore.c | 113 
> >> ++++++++++++++++++++++++++++++++++++++++----
> >>   2 files changed, 117 insertions(+), 10 deletions(-)
> >>
> >> diff --git a/tools/libxc/xc_sr_common.h b/tools/libxc/xc_sr_common.h
> >> index f8121e7..3bf27f1 100644
> >> --- a/tools/libxc/xc_sr_common.h
> >> +++ b/tools/libxc/xc_sr_common.h
> >> @@ -208,6 +208,20 @@ struct xc_sr_context
> >>               /* Plain VM, or checkpoints over time. */
> >>               bool checkpointed;
> >>
> >> +            /* Currently buffering records between a checkpoint */
> >> +            bool buffer_all_records;
> >> +
> >> +/*
> >> + * With Remus, we buffer the records sent by the primary at checkpoint,
> >> + * in case the primary will fail, we can recover from the last
> >> + * checkpoint state.
> >> + * This should be enough because primary only send dirty pages at
> >> + * checkpoint.
> >
> > I'm not sure how it then follows that 1024 buffers is guaranteed to be
> > enough, unless there is something on the sending side arranging it to be
> > so?
> 
> There are only few records at every checkpoint in my test, mostly under 10,
> probably because I don't do much operations in the Guest. I thought This limit
> can be adjusted later by further testing.

For some reason I thought these buffers included the page data, is that
not true? I was expecting the bulk of the records to be dirty page data.

> Since you and Andy both have doubts on this, I have to reconsider on this,
> perhaps there should be no limit. Even if the 1024 limit works for
> most of the cases, there might be cases that exceed the limit. So I will
> add another member 'allocated_rec_num' in the context, when the
> 'buffered_rec_num' exceed the 'allocated_rec_num', I will reallocate the 
> buffer.
> The initial buffer size will be 1024 records which will work for most cases.

That seems easy enough to be worth doing even if I was wrong about paged
data.



_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel