On Thu 20-02-20 12:33:13, Baoquan He wrote:
> Currently, subsection map is used when SPARSEMEM is enabled, including
> VMEMMAP case and !VMEMMAP case. However, subsection hotplug is not
> supported at all in SPARSEMEM|!VMEMMAP case, subsection map is unnecessary
> and misleading. Let's adjust code to only allow subsection map being
> used in VMEMMAP case.
This really needs more explanation I believe. What exactly happens if
somebody tries to hotremove a part of the section with !VMEMMAP? I can
see that clear_subsection_map returns 0 but that is not an error code.
Besides that section_deactivate doesn't propagate the error upwards.
/me stares into the code
OK, I can see it now. It is relying on check_pfn_span to use the proper
subsection granularity. This really begs for a comment in the code
somewhere.
>
> Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
> ---
> include/linux/mmzone.h | 2 ++
> mm/sparse.c | 20 ++++++++++++++++++++
> 2 files changed, 22 insertions(+)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 462f6873905a..fc0de3a9a51e 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -1185,7 +1185,9 @@ static inline unsigned long section_nr_to_pfn(unsigned long sec)
> #define SUBSECTION_ALIGN_DOWN(pfn) ((pfn) & PAGE_SUBSECTION_MASK)
>
> struct mem_section_usage {
> +#ifdef CONFIG_SPARSEMEM_VMEMMAP
> DECLARE_BITMAP(subsection_map, SUBSECTIONS_PER_SECTION);
> +#endif
> /* See declaration of similar field in struct zone */
> unsigned long pageblock_flags[0];
> };
> diff --git a/mm/sparse.c b/mm/sparse.c
> index df857ee9330c..66c497d6a229 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -209,6 +209,7 @@ static inline unsigned long first_present_section_nr(void)
> return next_present_section_nr(-1);
> }
>
> +#ifdef CONFIG_SPARSEMEM_VMEMMAP
> static void subsection_mask_set(unsigned long *map, unsigned long pfn,
> unsigned long nr_pages)
> {
> @@ -243,6 +244,11 @@ void __init subsection_map_init(unsigned long pfn, unsigned long nr_pages)
> nr_pages -= pfns;
> }
> }
> +#else
> +void __init subsection_map_init(unsigned long pfn, unsigned long nr_pages)
> +{
> +}
> +#endif
>
> /* Record a memory area against a node. */
> void __init memory_present(int nid, unsigned long start, unsigned long end)
> @@ -726,6 +732,7 @@ static void free_map_bootmem(struct page *memmap)
> }
> #endif /* CONFIG_SPARSEMEM_VMEMMAP */
>
> +#ifdef CONFIG_SPARSEMEM_VMEMMAP
> /**
> * clear_subsection_map - Clear subsection map of one memory region
> *
> @@ -764,6 +771,12 @@ static int clear_subsection_map(unsigned long pfn, unsigned long nr_pages)
>
> return 1;
> }
> +#else
> +static int clear_subsection_map(unsigned long pfn, unsigned long nr_pages)
> +{
> + return 0;
> +}
> +#endif
>
> static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
> struct vmem_altmap *altmap)
> @@ -820,6 +833,7 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
> ms->section_mem_map = (unsigned long)NULL;
> }
>
> +#ifdef CONFIG_SPARSEMEM_VMEMMAP
> /**
> * fill_subsection_map - fill subsection map of a memory region
> * @pfn - start pfn of the memory range
> @@ -854,6 +868,12 @@ static int fill_subsection_map(unsigned long pfn, unsigned long nr_pages)
>
> return rc;
> }
> +#else
> +static int fill_subsection_map(unsigned long pfn, unsigned long nr_pages)
> +{
> + return 0;
> +}
> +#endif
>
> static struct page * __meminit section_activate(int nid, unsigned long pfn,
> unsigned long nr_pages, struct vmem_altmap *altmap)
> --
> 2.17.2
>
--
Michal Hocko
SUSE Labs
