linux-kernel - Re: [PATCH v3 3/7] mm/sparse.c: introduce a new function clear_subsection

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Date:   Mon, 9 Mar 2020 21:32:18 +0800
From:   Baoquan He <bhe@...hat.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, mhocko@...e.com,
        richardw.yang@...ux.intel.com, dan.j.williams@...el.com,
        osalvador@...e.de, rppt@...ux.ibm.com
Subject: Re: [PATCH v3 3/7] mm/sparse.c: introduce a new function
 clear_subsection_map()

On 03/09/20 at 09:59am, David Hildenbrand wrote:
> On 07.03.20 09:42, Baoquan He wrote:
> > Factor out the code which clear subsection map of one memory region from
> > section_deactivate() into clear_subsection_map().
> > 
> > Signed-off-by: Baoquan He <bhe@...hat.com>
> > ---
> >  mm/sparse.c | 31 ++++++++++++++++++++++++-------
> >  1 file changed, 24 insertions(+), 7 deletions(-)
> > 
> > diff --git a/mm/sparse.c b/mm/sparse.c
> > index e37c0abcdc89..d9dcd58d5c1d 100644
> > --- a/mm/sparse.c
> > +++ b/mm/sparse.c
> > @@ -726,15 +726,11 @@ static void free_map_bootmem(struct page *memmap)
> >  }
> >  #endif /* CONFIG_SPARSEMEM_VMEMMAP */
> >  
> > -static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
> > -		struct vmem_altmap *altmap)
> > +static int clear_subsection_map(unsigned long pfn, unsigned long nr_pages)
> >  {
> >  	DECLARE_BITMAP(map, SUBSECTIONS_PER_SECTION) = { 0 };
> >  	DECLARE_BITMAP(tmp, SUBSECTIONS_PER_SECTION) = { 0 };
> >  	struct mem_section *ms = __pfn_to_section(pfn);
> > -	bool section_is_early = early_section(ms);
> > -	struct page *memmap = NULL;
> > -	bool empty = false;
> >  	unsigned long *subsection_map = ms->usage
> >  		? &ms->usage->subsection_map[0] : NULL;
> >  
> > @@ -745,8 +741,31 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
> >  	if (WARN(!subsection_map || !bitmap_equal(tmp, map, SUBSECTIONS_PER_SECTION),
> >  				"section already deactivated (%#lx + %ld)\n",
> >  				pfn, nr_pages))
> > +		return -EINVAL;
> > +
> > +	bitmap_xor(subsection_map, map, subsection_map, SUBSECTIONS_PER_SECTION);
> > +
> 
> Nit: I'd drop this line.

It's fine to me. I usually keep one line for the returning. I will
remove it when update.

> 
> > +	return 0;
> > +}
> > +
> > +static bool is_subsection_map_empty(struct mem_section *ms)
> > +{
> > +	return bitmap_empty(&ms->usage->subsection_map[0],
> > +			    SUBSECTIONS_PER_SECTION);
> > +}
> > +
> > +static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
> > +		struct vmem_altmap *altmap)
> > +{
> > +	struct mem_section *ms = __pfn_to_section(pfn);
> > +	bool section_is_early = early_section(ms);
> > +	struct page *memmap = NULL;
> > +	bool empty = false;
> 
> Nit: No need to initialize empty.

This is inherited from patch 1.

> 
> > +
> > +	if (clear_subsection_map(pfn, nr_pages))
> >  		return;
> >  
> 
> Nit: I'd drop this empty line.
> 
> > +	empty = is_subsection_map_empty(ms);
> >  	/*
> >  	 * There are 3 cases to handle across two configurations
> >  	 * (SPARSEMEM_VMEMMAP={y,n}):
> > @@ -764,8 +783,6 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
> >  	 *
> >  	 * For 2/ and 3/ the SPARSEMEM_VMEMMAP={y,n} cases are unified
> >  	 */
> > -	bitmap_xor(subsection_map, map, subsection_map, SUBSECTIONS_PER_SECTION);
> > -	empty = bitmap_empty(subsection_map, SUBSECTIONS_PER_SECTION);
> 
> I do wonder why you moved this up the comment?

Since this empty will cover two places of handling, so moved it up,
seems this is what I was thinking. Can move it back here.

> 
> >  	if (empty) {
> >  		unsigned long section_nr = pfn_to_section_nr(pfn);
> >  
> > 
> 
> Reviewed-by: David Hildenbrand <david@...hat.com>
> 
> -- 
> Thanks,
> 
> David / dhildenb