Re: [PATCH v2 4/6] util/oslib-posix: Avoid creating a single thread with MADV_POPULATE_WRITE

[David Hildenbrand]

On 27.07.21 21:04, Dr. David Alan Gilbert wrote:
> * David Hildenbrand (david@redhat.com) wrote:
> > Let's simplify the case when we only want a single thread and don't have
> > to mess with signal handlers.
> >
> > Signed-off-by: David Hildenbrand <david@redhat.com>
> > ---
> >   util/oslib-posix.c | 8 ++++++++
> >   1 file changed, 8 insertions(+)
> >
> > diff --git a/util/oslib-posix.c b/util/oslib-posix.c
> > index a1d309d495..1483e985c6 100644
> > --- a/util/oslib-posix.c
> > +++ b/util/oslib-posix.c
> > @@ -568,6 +568,14 @@ static bool touch_all_pages(char *area, size_t hpagesize, 
> > size_t numpages,
> >       }
> >   
> >       if (use_madv_populate_write) {
> > +        /* Avoid creating a single thread for MADV_POPULATE_WRITE */
> > +        if (context.num_threads == 1) {
> > +            if (qemu_madvise(area, hpagesize * numpages,
> > +                             QEMU_MADV_POPULATE_WRITE)) {
>
> Do you never have to fall back if this particular memory region is the
> one that can't do madv?

We sense upfront, when detecting use_madv_populate_write, whether it's 
supported on this very memory type. So, no need to fallback here.

> Dave

--
Thanks,

David / dhildenb