Re: [Qemu-devel] [PATCH 3/4] migration: ram: Switch to ram block writeback

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Beata Michalska (beata.michalska@linaro.org) wrote:
> On Tue, 10 Sep 2019 at 12:26, Dr. David Alan Gilbert
> <dgilbert@redhat.com> wrote:
> >
> > * Beata Michalska (beata.michalska@linaro.org) wrote:
> > > Switch to ram block writeback for pmem migration.
> > >
> > > Signed-off-by: Beata Michalska <beata.michalska@linaro.org>
> > > ---
> > >  migration/ram.c | 5 +----
> > >  1 file changed, 1 insertion(+), 4 deletions(-)
> > >
> > > diff --git a/migration/ram.c b/migration/ram.c
> > > index b01a37e7ca..8ea0bd63fc 100644
> > > --- a/migration/ram.c
> > > +++ b/migration/ram.c
> > > @@ -33,7 +33,6 @@
> > >  #include "qemu/bitops.h"
> > >  #include "qemu/bitmap.h"
> > >  #include "qemu/main-loop.h"
> > > -#include "qemu/pmem.h"
> > >  #include "xbzrle.h"
> > >  #include "ram.h"
> > >  #include "migration.h"
> > > @@ -4064,9 +4063,7 @@ static int ram_load_cleanup(void *opaque)
> > >      RAMBlock *rb;
> > >
> > >      RAMBLOCK_FOREACH_NOT_IGNORED(rb) {
> > > -        if (ramblock_is_pmem(rb)) {
> > > -            pmem_persist(rb->host, rb->used_length);
> > > -        }
> > > +        qemu_ram_block_writeback(rb);
> >
> > ACK for migration
> >
> > Although I do worry that if you really have pmem hardware, is it better
> > to fail the migration if you don't have libpmem available?
> 
> According to the PMDG man page, pmem_persist is supposed to be
> equivalent for the msync.

OK, but you do define qemu_ram_block_writeback to fall back to fdatasync;
so that would be too little?

> It's just more performant. So in case of real pmem hardware it should
> be all good.
> 
> [http://pmem.io/pmdk/manpages/linux/v1.2/libpmem.3.html]

Dave

> 
> BR
> Beata
> >
> > Dave
> >
> > >      }
> > >
> > >      xbzrle_load_cleanup();
> > > --
> > > 2.17.1
> > >
> > --
> > Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK