Re: [-mm PATCH] register_memory/unregister_memory clean ups

[Badari Pulavarty <pbadari@us.ibm.com>]

On Tue, 2008-02-12 at 14:15 -0800, Dave Hansen wrote:
> On Tue, 2008-02-12 at 14:07 -0800, Badari Pulavarty wrote:
> > On Tue, 2008-02-12 at 13:57 -0800, Dave Hansen wrote:
> > > On Tue, 2008-02-12 at 13:56 -0800, Badari Pulavarty wrote:
> > > > 
> > > > +static void __remove_section(struct zone *zone, unsigned long
> > > > section_nr)
> > > > +{
> > > > +       if (!valid_section_nr(section_nr))
> > > > +               return;
> > > > +
> > > > +       unregister_memory_section(__nr_to_section(section_nr));
> > > > +       sparse_remove_one_section(zone, section_nr);
> > > > +}
> > > 
> > > I do think passing in a mem_section* here is highly superior.  It makes
> > > it impossible to pass a pfn in and not get a warning.
> > > 
> > 
> > Only problem is, I need to hold pgdat_resize_lock() if pass *ms. 
> > If I don't hold the resize_lock, I have to re-evaluate.
> 
> What's wrong with holding the resize lock?  What races, precisely, are
> you trying to avoid?

I was trying to avoid holding resize lock for entire duration of
remove_section(), which includes removing sysfs entries etc. Its
needed only to decode and clear out sectionmap. (I am no longer 
passing pfns).

Whats wrong with passing section_nr ? It simply checks if that
section exists and if so removes sysfs entries and corresponding
sectionmap.  What wrong thing can happen ?

> 
> > And also,
> > I need to pass section_nr for decoding the mem_map anyway :(
> 
> See sparse.c::__section_nr().  It takes a mem_section* and returns a
> section_nr.

I know. It looked like a round about of getting section_nr while
we have that information easily available.

If you are really passionate about passing mem_section*, sure I
can do that :)

Thanks,
Badari