Re: [Qemu-devel] [PATCH v6 21/28] migration: setup ramstate for resume

[Dr. David Alan Gilbert]

* Peter Xu (address@hidden) wrote:
> On Tue, Feb 13, 2018 at 06:17:51PM +0000, Dr. David Alan Gilbert wrote:
> > * Peter Xu (address@hidden) wrote:
> > > After we updated the dirty bitmaps of ramblocks, we also need to update
> > > the critical fields in RAMState to make sure it is ready for a resume.
> > > 
> > > Signed-off-by: Peter Xu <address@hidden>
> > > ---
> > >  migration/ram.c        | 40 +++++++++++++++++++++++++++++++++++++++-
> > >  migration/trace-events |  1 +
> > >  2 files changed, 40 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/migration/ram.c b/migration/ram.c
> > > index a2a4b05d5c..d275875f54 100644
> > > --- a/migration/ram.c
> > > +++ b/migration/ram.c
> > > @@ -2250,6 +2250,36 @@ static int ram_init_all(RAMState **rsp)
> > >      return 0;
> > >  }
> > >  
> > > +static void ram_state_resume_prepare(RAMState *rs, QEMUFile *out)
> > > +{
> > > +    RAMBlock *block;
> > > +    long pages = 0;
> > > +
> > > +    /*
> > > +     * Postcopy is not using xbzrle/compression, so no need for that.
> > > +     * Also, since source are already halted, we don't need to care
> > > +     * about dirty page logging as well.
> > > +     */
> > > +
> > > +    RAMBLOCK_FOREACH(block) {
> > > +        pages += bitmap_count_one(block->bmap,
> > > +                                  block->used_length >> 
> > > TARGET_PAGE_BITS);
> > > +    }
> > > +
> > > +    /* This may not be aligned with current bitmaps. Recalculate. */
> > > +    rs->migration_dirty_pages = pages;
> > 
> > migration_dirty_pages is uint64_t - so we should probably do the cast
> > above and keep 'pages' as uint64_t.
> 
> Sure.
> 
> > 
> > > +    rs->last_seen_block = NULL;
> > > +    rs->last_sent_block = NULL;
> > > +    rs->last_page = 0;
> > > +    rs->last_version = ram_list.version;
> > 
> > Do you need to explicitly set
> >        rs->ram_bulk_stage = false;
> > 
> > if the failure happened just after the start of postcopy and no
> > requested pages had been sent, I think it might still  be set?
> 
> Could you elaborate what would go wrong even if it's still set?

I think it might start sending all pages rather than just those
that are dirty/needed;  see migration_bitmap_find_dirty.

Dave

> Thanks,
> 
> -- 
> Peter Xu
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK