Re: [Xen-devel] [PATCH v4 1/7] xen: introduce gnttab_max_nr_maptrack_frames command line option

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Fri, 10 Oct 2014, Jan Beulich wrote:
> >>> On 10.10.14 at 13:43, <stefano.stabellini@xxxxxxxxxxxxx> wrote:
> > --- a/docs/misc/xen-command-line.markdown
> > +++ b/docs/misc/xen-command-line.markdown
> > @@ -613,6 +613,12 @@ Specify the serial parameters for the GDB stub.
> >  
> >  Specify the maximum number of frames per grant table operation.
> >  
> > +### gnttab\_max\_nr\_maptrack\_frames
> 
> Do we really need the "nr_" in here?

I guess not


> > --- a/xen/common/grant_table.c
> > +++ b/xen/common/grant_table.c
> > @@ -102,10 +102,9 @@ nr_maptrack_frames(struct grant_table *t)
> >      return t->maptrack_limit / MAPTRACK_PER_PAGE;
> >  }
> >  
> > -static unsigned inline int max_nr_maptrack_frames(void)
> > -{
> > -    return (max_nr_grant_frames * MAX_MAPTRACK_TO_GRANTS_RATIO);
> > -}
> > +static unsigned int max_nr_maptrack_frames = DEFAULT_MAX_NR_GRANT_FRAMES *
> > +                                             MAX_MAPTRACK_TO_GRANTS_RATIO;
> > +integer_param("gnttab_max_nr_maptrack_frames", max_nr_maptrack_frames);
> 
> I'm not sure: As said before, the primary goal must be that existing
> setups don't suddenly start failing. I.e. the other options no longer
> controlling the maptrack table size may badly affect Dom0. One
> possibility would be to honor the other option in the original way if
> the new option wasn't made use of (and perhaps issue a warning
> to that effect).

Honestly I think that it would be a bad idea to try to second guess what
the user really meant with the options she passed. Also I think it is a
bad idea to have options do different things depending on the presence
or absence of other options.

I think we should either:

- leave things as they are
- add this new option and as a consequence also change the effect of
gnttab_max_nr_frames

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