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SubjectRe: [PATCH v3 5/7] mm/sparse.c: add note about only VMEMMAP supporting sub-section support
On 03/07/20 at 04:42pm, Baoquan He wrote:

Sorry, the subject should be:

mm/sparse.c: add note about only VMEMMAP supporting sub-section hotplug

> And tell check_pfn_span() gating the porper alignment and size of
> hot added memory region.
>
> And also move the code comments from inside section_deactivate()
> to being above it. The code comments are reasonable for the whole
> function, and the moving makes code cleaner.
>
> Signed-off-by: Baoquan He <bhe@redhat.com>
> ---
> mm/sparse.c | 37 ++++++++++++++++++++-----------------
> 1 file changed, 20 insertions(+), 17 deletions(-)
>
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 2142045ab5c5..0fbd79c4ad81 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -772,6 +772,22 @@ static bool is_subsection_map_empty(struct mem_section *ms)
> }
> #endif
>
> +/*
> + * To deactivate a memory region, there are 3 cases to handle across
> + * two configurations (SPARSEMEM_VMEMMAP={y,n}):
> + *
> + * 1. deactivation of a partial hot-added section (only possible in
> + * the SPARSEMEM_VMEMMAP=y case).
> + * a) section was present at memory init.
> + * b) section was hot-added post memory init.
> + * 2. deactivation of a complete hot-added section.
> + * 3. deactivation of a complete section from memory init.
> + *
> + * For 1, when subsection_map does not empty we will not be freeing the
> + * usage map, but still need to free the vmemmap range.
> + *
> + * For 2 and 3, the SPARSEMEM_VMEMMAP={y,n} cases are unified
> + */
> static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
> struct vmem_altmap *altmap)
> {
> @@ -784,23 +800,6 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
> return;
>
> empty = is_subsection_map_empty(ms);
> - /*
> - * There are 3 cases to handle across two configurations
> - * (SPARSEMEM_VMEMMAP={y,n}):
> - *
> - * 1/ deactivation of a partial hot-added section (only possible
> - * in the SPARSEMEM_VMEMMAP=y case).
> - * a/ section was present at memory init
> - * b/ section was hot-added post memory init
> - * 2/ deactivation of a complete hot-added section
> - * 3/ deactivation of a complete section from memory init
> - *
> - * For 1/, when subsection_map does not empty we will not be
> - * freeing the usage map, but still need to free the vmemmap
> - * range.
> - *
> - * For 2/ and 3/ the SPARSEMEM_VMEMMAP={y,n} cases are unified
> - */
> if (empty) {
> unsigned long section_nr = pfn_to_section_nr(pfn);
>
> @@ -907,6 +906,10 @@ static struct page * __meminit section_activate(int nid, unsigned long pfn,
> *
> * This is only intended for hotplug.
> *
> + * Note that only VMEMMAP supports sub-section aligned hotplug,
> + * the proper alignment and size are gated by check_pfn_span().
> + *
> + *
> * Return:
> * * 0 - On success.
> * * -EEXIST - Section has been present.
> --
> 2.17.2
>

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