* Juan Quintela (quint...@redhat.com) wrote:
> "Dr. David Alan Gilbert (git)" <dgilb...@redhat.com> wrote:
> > From: "Dr. David Alan Gilbert" <dgilb...@redhat.com>
> >
> > Where postcopy is preceeded by a period of precopy, the destination will
> > have received pages that may have been dirtied on the source after the
> > page was sent. The destination must throw these pages away before
> > starting it's CPUs.
> >
> > Maintain a 'sentmap' of pages that have already been sent.
> > Calculate list of sent & dirty pages
> > Provide helpers on the destination side to discard these.
> >
> > Signed-off-by: Dr. David Alan Gilbert <dgilb...@redhat.com>
>
> Not a patch without a suggestion O:-)
>
> > ---
> > include/migration/migration.h | 12 +++
> > include/migration/postcopy-ram.h | 35 +++++++
> > include/qemu/typedefs.h | 1 +
> > migration/migration.c | 1 +
> > migration/postcopy-ram.c | 108 +++++++++++++++++++++
> > migration/ram.c | 203
> > ++++++++++++++++++++++++++++++++++++++-
> > migration/savevm.c | 2 -
> > trace-events | 5 +
> > 8 files changed, 363 insertions(+), 4 deletions(-)
> >
> > diff --git a/include/migration/migration.h b/include/migration/migration.h
> > index 2a22381..4c6cf95 100644
> > --- a/include/migration/migration.h
> > +++ b/include/migration/migration.h
> > @@ -114,6 +114,13 @@ struct MigrationState
> >
> > /* Flag set once the migration has been asked to enter postcopy */
> > bool start_postcopy;
> > +
> > + /* bitmap of pages that have been sent at least once
> > + * only maintained and used in postcopy at the moment
> > + * where it's used to send the dirtymap at the start
> > + * of the postcopy phase
> > + */
> > + unsigned long *sentmap;
> > };
>
> We can use this sentmap for zero page optimization. If page is on
> sentmap, we need to sent a zero page, otherwise, just sent sentmap at
> the end of migration and clean everything not there?
Just as a compact way of sending zero pages? I'm not sure it would help.
> > +/*
> > + * Discard the contents of memory start..end inclusive.
> > + * We can assume that if we've been called postcopy_ram_hosttest returned
> > true
> > + */
> > +int postcopy_ram_discard_range(MigrationIncomingState *mis, uint8_t *start,
> > + uint8_t *end)
> > +{
> > + trace_postcopy_ram_discard_range(start, end);
> > + if (madvise(start, (end-start)+1, MADV_DONTNEED)) {
>
> Can we s/end/lenght/ and adjust everywhere?
Done - partially; everything that works in bytes is now start & length,
everything that works in indexes into the RAM bitmap is still start/end,
since generally that's what they're working with already.
> Not here, but putting a comment explaining where magic 12 cames from on
> definition of constant?
Done.
> I think that the sentbitmap bits could we used without the rest.
Possibly, I can kind of see it's useful - but I'm not convinced what else for
yet.
Dave
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
