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SubjectRe: [PATCH 2/2] mm,memory_hotplug: Fix shrink_{zone,node}_span
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Oscar Salvador <osalvador@suse.de> writes:

> Since [1], shrink_{zone,node}_span work on PAGES_PER_SUBSECTION granularity.
> The problem is that deactivation of the section occurs later on in
> sparse_remove_section, so pfn_valid()->pfn_section_valid() will always return
> true before we deactivate the {sub}section.

Can you explain this more? The patch doesn't update section_mem_map
update sequence. So what changed? What is the problem in finding
pfn_valid() return true there?

>
> I spotted this during hotplug hotremove tests, there I always saw that
> spanned_pages was, at least, left with PAGES_PER_SECTION, even if we
> removed all memory linked to that zone.
>
> Fix this by decoupling section_deactivate from sparse_remove_section, and
> re-order the function calls.
>
> Now, __remove_section will:
>
> 1) deactivate section
> 2) shrink {zone,node}'s pages
> 3) remove section
>
> [1] https://patchwork.kernel.org/patch/11003467/
>
> Fixes: mmotm ("mm/hotplug: prepare shrink_{zone, pgdat}_span for sub-section removal")
> Signed-off-by: Oscar Salvador <osalvador@suse.de>
> ---
> include/linux/memory_hotplug.h | 7 ++--
> mm/memory_hotplug.c | 6 +++-
> mm/sparse.c | 77 +++++++++++++++++++++++++++++-------------
> 3 files changed, 62 insertions(+), 28 deletions(-)
>
> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
> index f46ea71b4ffd..d2eb917aad5f 100644
> --- a/include/linux/memory_hotplug.h
> +++ b/include/linux/memory_hotplug.h
> @@ -348,9 +348,10 @@ extern void move_pfn_range_to_zone(struct zone *zone, unsigned long start_pfn,
> extern bool is_memblock_offlined(struct memory_block *mem);
> extern int sparse_add_section(int nid, unsigned long pfn,
> unsigned long nr_pages, struct vmem_altmap *altmap);
> -extern void sparse_remove_section(struct mem_section *ms,
> - unsigned long pfn, unsigned long nr_pages,
> - unsigned long map_offset, struct vmem_altmap *altmap);
> +int sparse_deactivate_section(unsigned long pfn, unsigned long nr_pages);
> +void sparse_remove_section(unsigned long pfn, unsigned long nr_pages,
> + unsigned long map_offset, struct vmem_altmap *altmap,
> + int section_empty);
> extern struct page *sparse_decode_mem_map(unsigned long coded_mem_map,
> unsigned long pnum);
> extern bool allow_online_pfn_range(int nid, unsigned long pfn, unsigned long nr_pages,
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index b9ba5b85f9f7..03d535eee60d 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -517,12 +517,16 @@ static void __remove_section(struct zone *zone, unsigned long pfn,
> struct vmem_altmap *altmap)
> {
> struct mem_section *ms = __nr_to_section(pfn_to_section_nr(pfn));
> + int ret;
>
> if (WARN_ON_ONCE(!valid_section(ms)))
> return;
>
> + ret = sparse_deactivate_section(pfn, nr_pages);
> __remove_zone(zone, pfn, nr_pages);
> - sparse_remove_section(ms, pfn, nr_pages, map_offset, altmap);
> + if (ret >= 0)
> + sparse_remove_section(pfn, nr_pages, map_offset, altmap,
> + ret);
> }
>
> /**
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 1e224149aab6..d4953ee1d087 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -732,16 +732,47 @@ 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)
> +static void section_remove(unsigned long pfn, unsigned long nr_pages,
> + struct vmem_altmap *altmap, int section_empty)
> +{
> + struct mem_section *ms = __pfn_to_section(pfn);
> + bool section_early = early_section(ms);
> + struct page *memmap = NULL;
> +
> + if (section_empty) {
> + unsigned long section_nr = pfn_to_section_nr(pfn);
> +
> + if (!section_early) {
> + kfree(ms->usage);
> + ms->usage = NULL;
> + }
> + memmap = sparse_decode_mem_map(ms->section_mem_map, section_nr);
> + ms->section_mem_map = sparse_encode_mem_map(NULL, section_nr);
> + }
> +
> + if (section_early && memmap)
> + free_map_bootmem(memmap);
> + else
> + depopulate_section_memmap(pfn, nr_pages, altmap);
> +}
> +
> +/**
> + * section_deactivate: Deactivate a {sub}section.
> + *
> + * Return:
> + * * -1 - {sub}section has already been deactivated.
> + * * 0 - Section is not empty
> + * * 1 - Section is empty
> + */
> +
> +static int section_deactivate(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;
> + int section_empty = 0;
>
> subsection_mask_set(map, pfn, nr_pages);
> if (subsection_map)
> @@ -750,7 +781,7 @@ 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 -1;
>
> /*
> * There are 3 cases to handle across two configurations
> @@ -770,21 +801,10 @@ 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)) {
> - unsigned long section_nr = pfn_to_section_nr(pfn);
> -
> - if (!section_is_early) {
> - kfree(ms->usage);
> - ms->usage = NULL;
> - }
> - memmap = sparse_decode_mem_map(ms->section_mem_map, section_nr);
> - ms->section_mem_map = sparse_encode_mem_map(NULL, section_nr);
> - }
> + if (bitmap_empty(subsection_map, SUBSECTIONS_PER_SECTION))
> + section_empty = 1;
>
> - if (section_is_early && memmap)
> - free_map_bootmem(memmap);
> - else
> - depopulate_section_memmap(pfn, nr_pages, altmap);
> + return section_empty;
> }
>
> static struct page * __meminit section_activate(int nid, unsigned long pfn,
> @@ -834,7 +854,11 @@ static struct page * __meminit section_activate(int nid, unsigned long pfn,
>
> memmap = populate_section_memmap(pfn, nr_pages, nid, altmap);
> if (!memmap) {
> - section_deactivate(pfn, nr_pages, altmap);
> + int ret;
> +
> + ret = section_deactivate(pfn, nr_pages);
> + if (ret >= 0)
> + section_remove(pfn, nr_pages, altmap, ret);
> return ERR_PTR(-ENOMEM);
> }
>
> @@ -919,12 +943,17 @@ static inline void clear_hwpoisoned_pages(struct page *memmap, int nr_pages)
> }
> #endif
>
> -void sparse_remove_section(struct mem_section *ms, unsigned long pfn,
> - unsigned long nr_pages, unsigned long map_offset,
> - struct vmem_altmap *altmap)
> +int sparse_deactivate_section(unsigned long pfn, unsigned long nr_pages)
> +{
> + return section_deactivate(pfn, nr_pages);
> +}
> +
> +void sparse_remove_section(unsigned long pfn, unsigned long nr_pages,
> + unsigned long map_offset, struct vmem_altmap *altmap,
> + int section_empty)
> {
> clear_hwpoisoned_pages(pfn_to_page(pfn) + map_offset,
> nr_pages - map_offset);
> - section_deactivate(pfn, nr_pages, altmap);
> + section_remove(pfn, nr_pages, altmap, section_empty);
> }
> #endif /* CONFIG_MEMORY_HOTPLUG */
> --
> 2.12.3

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