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

Baoquan He
2020-03-03T08:22:17Z

On 03/02/20 at 04:43pm, David Hildenbrand wrote:
> On 01.03.20 06:20, Baoquan He wrote:
> > 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.
> >
>
> Something like this on top would be easier to understand IMHO
>
>
> diff --git a/mm/sparse.c b/mm/sparse.c
> index dc79b00ddaaa..be5c80e9cfee 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -726,20 +726,6 @@ static void free_map_bootmem(struct page *memmap)
> }
> #endif /* CONFIG_SPARSEMEM_VMEMMAP */
>
> -/**
> - * 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.
> - */
> static int clear_subsection_map(unsigned long pfn, unsigned long nr_pages)
> {
> DECLARE_BITMAP(map, SUBSECTIONS_PER_SECTION) = { 0 };
> @@ -758,11 +744,12 @@ static int clear_subsection_map(unsigned long pfn, unsigned long nr_pages)
> return -EINVAL;
>
> bitmap_xor(subsection_map, map, subsection_map, SUBSECTIONS_PER_SECTION);
> + return 0;
> +}
>
> - if (bitmap_empty(subsection_map, SUBSECTIONS_PER_SECTION))
> - return 0;
> -
> - return 1;
> +static bool is_subsection_map_empty(unsigned long pfn, unsigned long nr_pages)
> +{
> + return bitmap_empty(subsection_map, SUBSECTIONS_PER_SECTION);
> }
>
> static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
> @@ -771,11 +758,8 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
> struct mem_section *ms = __pfn_to_section(pfn);
> bool section_is_early = early_section(ms);
> struct page *memmap = NULL;
> - int rc;
> -
>
> - rc = clear_subsection_map(pfn, nr_pages);
> - if (IS_ERR_VALUE((unsigned long)rc))
> + if (unlikely(clear_subsection_map(pfn, nr_pages)))
> return;
> /*
> * There are 3 cases to handle across two configurations
> @@ -794,7 +778,7 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
> *
> * For 2/ and 3/ the SPARSEMEM_VMEMMAP={y,n} cases are unified
> */
> - if (!rc) {
> + if (is_subsection_map_empty(pfn, nr_pages)) {
> unsigned long section_nr = pfn_to_section_nr(pfn);

Tried this way, it's not good in this patch. Since ms->usage might be
freed in this place.

if (!PageReserved(virt_to_page(ms->usage))) {
kfree(ms->usage);
ms->usage = NULL;
}

If have to introduce is_subsection_map_empty(), the code need be
adjusted a little bit. It may need be done in another separate patch to
adjust it. If you agree, I would like to keep this patch as is, later
I can refactor this on top of this patchset, or if anyone else post
patch to adjust it, I can help review.

>
> /*
> @@ -816,7 +800,7 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
> else
> depopulate_section_memmap(pfn, nr_pages, altmap);
>
> - if (!rc)
> + if (is_subsection_map_empty(pfn, nr_pages))
> ms->section_mem_map = (unsigned long)NULL;
> }
>
>
> --
> Thanks,
>
> David / dhildenb