Re: [Qemu-devel] [PATCH 1/2] migration: bitmap_set is unnecessary as bitmap_new uses g_try_malloc0

[Denis V. Lunev]

On 09/25/2015 12:24 PM, Wen Congyang wrote:
> On 09/25/2015 05:09 PM, Denis V. Lunev wrote:
> > we can omit calling of bitmap_set in migration_bitmap_extend and
> > ram_save_setup just after bitmap_new, which properly zeroes memory
> > inside.
> This patch is wrong. bitmap_set() is set all bits of the memory to 1,
> not 0.

OK, then I'll replace g_try_malloc0 with g_try_malloc in the next patch 
to avoid
double memset

> > Signed-off-by: Denis V. Lunev <address@hidden>
> > CC: Igor Redko <address@hidden>
> > CC: Anna Melekhova <address@hidden>
> > CC: Juan Quintela <address@hidden>
> > CC: Amit Shah <address@hidden>
> > CC: Wen Congyang <address@hidden>
> > ---
> >   migration/ram.c | 2 --
> >   1 file changed, 2 deletions(-)
> >
> > diff --git a/migration/ram.c b/migration/ram.c
> > index 7f007e6..a712c68 100644
> > --- a/migration/ram.c
> > +++ b/migration/ram.c
> > @@ -1081,7 +1081,6 @@ void migration_bitmap_extend(ram_addr_t old, ram_addr_t 
> > new)
> >            */
> >           qemu_mutex_lock(&migration_bitmap_mutex);
> >           bitmap_copy(bitmap, old_bitmap, old);
> > -        bitmap_set(bitmap, old, new - old);
> >           atomic_rcu_set(&migration_bitmap, bitmap);
> >           qemu_mutex_unlock(&migration_bitmap_mutex);
> >           migration_dirty_pages += new - old;
> > @@ -1146,7 +1145,6 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
> >   
> >       ram_bitmap_pages = last_ram_offset() >> TARGET_PAGE_BITS;
> >       migration_bitmap = bitmap_new(ram_bitmap_pages);
> > -    bitmap_set(migration_bitmap, 0, ram_bitmap_pages);
> >   
> >       /*
> >        * Count the total number of pages used by ram blocks not including any