linux-kernel - Re: [PATCH 1/7] mm/sparse.c: Introduce new function fill_subsection

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Date:   Tue, 11 Feb 2020 20:46:48 +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, dan.j.williams@...el.com,
        richardw.yang@...ux.intel.com
Subject: Re: [PATCH 1/7] mm/sparse.c: Introduce new function
 fill_subsection_map()

On 02/10/20 at 10:49am, David Hildenbrand wrote:
> On 09.02.20 11:48, Baoquan He wrote:
> > Wrap the codes filling subsection map in section_activate() into
> > fill_subsection_map(), this makes section_activate() cleaner and
> > easier to follow.
> > 
> > Signed-off-by: Baoquan He <bhe@...hat.com>
> > ---
> >  mm/sparse.c | 45 ++++++++++++++++++++++++++++++++++-----------
> >  1 file changed, 34 insertions(+), 11 deletions(-)
> > 
> > diff --git a/mm/sparse.c b/mm/sparse.c
> > index c184b69460b7..9ad741ccbeb6 100644
> > --- a/mm/sparse.c
> > +++ b/mm/sparse.c
> > @@ -788,24 +788,28 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
> >  		depopulate_section_memmap(pfn, nr_pages, altmap);
> >  }
> >  
> > -static struct page * __meminit section_activate(int nid, unsigned long pfn,
> > -		unsigned long nr_pages, struct vmem_altmap *altmap)
> > +/**
> > + * fill_subsection_map - fill subsection map of a memory region
> > + * @pfn - start pfn of the memory range
> > + * @nr_pages - number of pfns to add in the region
> > + *
> > + * This clears the related subsection map inside one section, and only
> > + * intended for hotplug.
> > + *
> > + * Return:
> > + * * 0		- On success.
> > + * * -EINVAL	- Invalid memory region.
> > + * * -EEXIST	- Subsection map has been set.
> > + */
> > +static int fill_subsection_map(unsigned long pfn, unsigned long nr_pages)
> >  {
> > -	DECLARE_BITMAP(map, SUBSECTIONS_PER_SECTION) = { 0 };
> >  	struct mem_section *ms = __pfn_to_section(pfn);
> > -	struct mem_section_usage *usage = NULL;
> > +	DECLARE_BITMAP(map, SUBSECTIONS_PER_SECTION) = { 0 };
> >  	unsigned long *subsection_map;
> > -	struct page *memmap;
> >  	int rc = 0;
> >  
> >  	subsection_mask_set(map, pfn, nr_pages);
> >  
> > -	if (!ms->usage) {
> > -		usage = kzalloc(mem_section_usage_size(), GFP_KERNEL);
> > -		if (!usage)
> > -			return ERR_PTR(-ENOMEM);
> > -		ms->usage = usage;
> > -	}
> >  	subsection_map = &ms->usage->subsection_map[0];
> >  
> >  	if (bitmap_empty(map, SUBSECTIONS_PER_SECTION))
> > @@ -816,6 +820,25 @@ static struct page * __meminit section_activate(int nid, unsigned long pfn,
> >  		bitmap_or(subsection_map, map, subsection_map,
> >  				SUBSECTIONS_PER_SECTION);
> >  
> > +	return rc;
> > +}
> > +
> > +static struct page * __meminit section_activate(int nid, unsigned long pfn,
> > +		unsigned long nr_pages, struct vmem_altmap *altmap)
> > +{
> > +	struct mem_section *ms = __pfn_to_section(pfn);
> > +	struct mem_section_usage *usage = NULL;
> > +	struct page *memmap;
> > +	int rc = 0;
> > +
> > +	if (!ms->usage) {
> > +		usage = kzalloc(mem_section_usage_size(), GFP_KERNEL);
> > +		if (!usage)
> > +			return ERR_PTR(-ENOMEM);
> > +		ms->usage = usage;
> > +	}
> > +
> > +	rc = fill_subsection_map(pfn, nr_pages);
> >  	if (rc) {
> >  		if (usage)
> >  			ms->usage = NULL;
> > 
> 
> What about having two variants of
> section_activate()/section_deactivate() instead? Then we don't have any
> subsection related stuff in !subsection code.

Thanks for looking into this, David.

Having two variants of section_activate()/section_deactivate() is also
good. Just not like memmap handling which is very different between classic
sparse and vmemmap, makes having two variants very attractive, the code
and logic in section_activate()/section_deactivate() is not too much,
and both of them basically can share the most of code, these make the
variants way not so necessary. I personally prefer the current way, what
do you think?

Thanks
Baoquan