Re: [PATCH v2 3/7] mm/sparse.c: introduce a new function clear_subsection_map()

Baoquan He
2020-03-01T05:21:17Z

On 02/28/20 at 03:36pm, David Hildenbrand wrote:
> On 20.02.20 05:33, Baoquan He wrote:
> > Wrap the codes which clear subsection map of one memory region from
> > section_deactivate() into clear_subsection_map().
> >
> > Signed-off-by: Baoquan He <bhe@redhat.com>
> > ---
> > mm/sparse.c | 46 ++++++++++++++++++++++++++++++++++++++--------
> > 1 file changed, 38 insertions(+), 8 deletions(-)
> >
> > diff --git a/mm/sparse.c b/mm/sparse.c
> > index 977b47acd38d..df857ee9330c 100644
> > --- a/mm/sparse.c
> > +++ b/mm/sparse.c
> > @@ -726,14 +726,25 @@ 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)
> > +/**
> > + * clear_subsection_map - Clear subsection map of one memory region
> > + *
> > + * @pfn - start pfn of the memory range
> > + * @nr_pages - number of pfns to add in the region
> > + *
> > + * This is only intended for hotplug, and clear the related subsection
> > + * map inside one section.
> > + *
> > + * Return:
> > + * * -EINVAL - Section already deactived.
> > + * * 0 - Subsection map is emptied.
> > + * * 1 - Subsection map is not empty.
> > + */
>
> Less verbose please (in my preference: none and simplify return handling)
>
> > +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;
> > unsigned long *subsection_map = ms->usage
> > ? &ms->usage->subsection_map[0] : NULL;
> >
> > @@ -744,8 +755,28 @@ 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;
> > + return -EINVAL;
> > +
> > + bitmap_xor(subsection_map, map, subsection_map, SUBSECTIONS_PER_SECTION);
> >
> > + if (bitmap_empty(subsection_map, SUBSECTIONS_PER_SECTION))
> > + return 0;
> > +
>
> Can we please just have a
>
> subsection_map_empty() instead and handle that in the caller?
> (you can then always return true in the !VMEMMAP variant)

I don't follow. Could you be more specific? or pseudo code please?

The old code has to handle below case in which subsection_map has been
cleared. And I introduce clear_subsection_map() to encapsulate all
subsection map realted code so that !VMEMMAP won't have to see it any
more.

if (WARN(!subsection_map || !bitmap_equal(tmp, map, SUBSECTIONS_PER_SECTION),
"section already deactivated (%#lx + %ld)\n",
pfn, nr_pages))
return;

>
> I dislike the "rc" handling in the caller.
>
> > + return 1;
> > +}
> > +
> > +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;
> > + int rc;
> > +
> > +
>
> one superfluous empty line
>
> > + rc = clear_subsection_map(pfn, nr_pages);
> > + if (IS_ERR_VALUE((unsigned long)rc))
>
> huh? "if (rc < 0)" ? or am I missing something?

Both is fine to me, I have no preference, can change like this.

>
> > + return;
> > /*
> > * There are 3 cases to handle across two configurations
> > * (SPARSEMEM_VMEMMAP={y,n}):
> > @@ -763,8 +794,7 @@ 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);
> > - if (bitmap_empty(subsection_map, SUBSECTIONS_PER_SECTION)) {
> > + if (!rc) {
> > unsigned long section_nr = pfn_to_section_nr(pfn);
> >
> > /*
> > @@ -786,7 +816,7 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
> > else
> > depopulate_section_memmap(pfn, nr_pages, altmap);
> >
> > - if (bitmap_empty(subsection_map, SUBSECTIONS_PER_SECTION))
> > + if (!rc)
>
> I don't really like that handling.
>
> Either
>
> s/rc/section_empty/
>
> or use a separate subsection_map_empty()
>
> > ms->section_mem_map = (unsigned long)NULL;
> > }
> >
> >
>
> Thanks!
>
> --
> Thanks,
>
> David / dhildenb