linux-kernel - Re: [-mm PATCH] register_memory/unregister

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Message-Id: <1202856720.25604.69.camel@dyn9047017100.beaverton.ibm.com>
Date:	Tue, 12 Feb 2008 14:51:59 -0800
From:	Badari Pulavarty <pbadari@...ibm.com>
To:	Dave Hansen <haveblue@...ibm.com>
Cc:	Yasunori Goto <y-goto@...fujitsu.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	lkml <linux-kernel@...r.kernel.org>, greg@...ah.com,
	linux-mm <linux-mm@...ck.org>
Subject: Re: [-mm PATCH] register_memory/unregister_memory clean ups

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

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