Re: [PATCH v2 4/7] mm/sparse.c: only use subsection map in VMEMMAP case

[Wei Yang]

On Thu, Feb 20, 2020 at 12:33:13PM +0800, 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.
>
>Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>

Reviewed-by: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx>

>---
> 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

-- 
Wei Yang
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